Term
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Definition
| the study of the distribution and determinants of disease frequency in the human population and the applications of this study to control health problems |
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Term
| epidemiology v. clinical medicine |
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Definition
epidemiology deals with the entire population by preventing disease and promoting health
clinical medicine deals with individuals improving treatments |
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Term
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Definition
John Graunt - count people who died
James Lind - studies could test epi
William Farr - founder of modern epi
John Snow - investigated contaminated water
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Term
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Definition
| analysis of disease patterns according to person, place, and time |
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Term
| uses of descriptive epidemiology |
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Definition
1. to search for clues about the cause of disease and generate hypotheses
2. for administrators and planners to prepare for public health issues
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Term
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Definition
measures the frequency of existing disease
the proportion of the total population that is diseased |
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Term
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Definition
the proportion of the population that is diseased at a single point in time
number of existing cases/number in total population at a point in time |
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Term
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Definition
the proportion of the population that is diseased during a specified duration of time
number of existing cases/number in total population during a period of time |
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Term
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Definition
the proportion of a candidate population that becomes diseased over a specified period of time
range 0 to 1
number of new cases/number in candidate population |
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Term
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Definition
the occurence of new case of disease that arise during person-time of observation.
number of new cases/person-time of observation in candidate population |
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Term
| What measures the risk of developing a disease? |
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Definition
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Term
| Relationship of incidence and prevalence |
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Definition
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Term
| What is used to evaluate the effectiveness of programs that try to prevent disease and by researchers studying the cause of a disease? |
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Definition
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Term
| Used to estimated the needs of medical facilities |
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Definition
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Term
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Definition
total number of deaths from all causes per 100,000 population
(number of deaths/average pop) x1000 |
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Term
| cause-specific mortality rate |
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Definition
| (number of deaths due to a cause/population) x 10000 |
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Term
| age-specific mortality rate |
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Definition
| (number of deaths in a given age group / number of people in that age group) x 1000 |
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Term
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Definition
| number of deaths of infants less than a year of age for a year over 1000 livebirths |
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Term
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Definition
| number of existing or new cases of a particular disease or condition per 1000 population |
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Term
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Definition
number of cases of disease that develop during defined period divided by number in population at risk at start of period
used in infectious disease outbreaks to determine how pathegentic a disease is. |
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Term
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Definition
number of deaths per number of cases of disease with a specified amount of time
type of cumulative incidence rate |
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Term
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Definition
| group of people with a common characteristic like age, race, sex, place of residence, religion, or use of hospital services |
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Term
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Definition
membership is permanent and defined by an event
exposed to radiation from Chornobyl |
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Term
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Definition
| membership is transient and defined by being in or out of a "state" |
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Term
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Definition
First step in study
How are you going to measure the disease occurence and evaluate its risk factors. |
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Term
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Definition
Number of individuals affected with the disease (numerator)
Size of source population (denominator)
Length of time the population was followed (time period |
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Term
Three types of frequency measures
1. Ratio
2. Proportion
3. Rate |
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Definition
1. division of one number by another, number don't have to be related
2. numerator is subset of denominator, often expressed as a percentage
3. time is an intrinsic part of the denominator |
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Term
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Definition
When Incidence = Duration
examined for policy and planning |
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Term
| What is the best indicator for determining the effectiveness of a new treatment? |
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Definition
| mortality rate and prevalence |
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Term
| What is the best indicator for evaluating the effectiveness of a program that tries to prevent the disease? |
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Definition
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Term
| What is the best indicator for estimating the needs for medical facilities in treating the disease? |
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Definition
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Term
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Definition
| Rate or risk in exposed group over the rate or risk in unexposed group |
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Term
| What does a relative risk of 1 indicate? |
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Definition
| no association between exposure and disease |
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Term
What does a relative risk of 1.6 mean?
What does a relative risk of 0.6 mean? |
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Definition
1.6 times the risk or 60% increased risk of the disease
.4 times the risk of the disease or 40% less risk |
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Term
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Definition
used to compare disease occurence among the exposed with the disease occurence among the unexposed
subtract one measurement from the other |
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Term
| Purposes of Risk/Rate Difference |
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Definition
1. absolue effect of exposure
2. shows the excess disease risk in the exposed group compared to the unexposed group
3. shows the public health impact of an exposure |
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Term
| Purpose of Population Risk/Rate Differnce |
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Definition
Measures the excess disease occurrence among the total population that is associated with the exposure.
Helps to evaluate which exposures are most relevant to the health of a target population |
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Term
| What is the problem with crude rates? |
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Definition
| Difficult to interpret because groups may differ on age, gender, race, etc. that can distort these measures. |
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Term
| How can crude rates be "fixed"? |
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Definition
1. direct method of standardization
2. indirect method of standardization |
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Term
| What method of standardization of crude rates that uses adjusted rates by group (age) and total population numbers? |
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Definition
| Direct method of standardization |
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Term
| What method of standardization uses population by groups (age) and crude rates? |
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Definition
| Indirect method of standardization |
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Term
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Definition
Identification of an unrecognized disease or defect by the application of tests, exams, or other procedures.
Classifies asymptomatic people as likely or unlikely to have a disease or defect
Finds people before symptoms occur. |
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Term
| What is the purpose of screening |
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Definition
To delay the onset of symptomatic or clinical disease.
Early detection and treatment will improve disease prognosis and survival |
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Term
| What is primary prevention? |
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Definition
| The maintenance of health through individual or community efforts so that the disease process never starts |
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Term
| What is secondary prevention? |
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Definition
| The reduction in the expression and severity of clinical disease by identifying asymptomatic individuals during the window between onset and clinical symptoms |
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Term
| What is needed for a successful screening? |
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Definition
1. Suitable disease
2. Suitable diagnostic or screening test
3. A suitable screening program |
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Term
| What are the characteristics of a suitable disease for screening? |
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Definition
1. Has serious clinical and public health consequences
2. Is progressive
3. Normally there needs to be an effective treatment (exception HIV)
4. Disease treatment must be effective at an early stage (don't detect without reason)
5. Prevalence of the detectable pre-clinical phase must be high (like 5%)
6. Natural history of disease should be known |
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Term
| Natural history of a disease |
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Definition
The stages of disease progression
From biologic onset through clinical symptoms to resul (death) |
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Term
| Total pre-clinical phase of a disease |
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Definition
| The time symptoms develop minus the time of biological change |
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Term
| Detectable pre-clinical phase (DPCP) of a disease |
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Definition
| the time symptoms develop minus the time a disease is detectable |
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Term
| What factors make Detectable pre-clinical phase (DPCP) vary? |
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Definition
The test
the disease
the individual |
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Term
Lead time
(due to screening) |
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Definition
| the amount of time by which the diagnosis is advanced as a result of screening |
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Term
| What are the characteristics of a suitable screening test? |
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Definition
1. inexpensive
2. easy to administer
3. has high level of patient acceptability (not too painful or intrusive)
4. has a high level of validity (accurately measures disease) and reliability (consistently produces the same results)
*validity is more important than reliability |
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Term
| What is caused by high validity but low reliability? |
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Definition
| Large variation around the mean |
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Term
| What is caused by low validity by high reliability? |
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Definition
| small variation but not accurate |
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Term
| What measure answers the question "If I have the dissease, what is the likelihood of testing positive on a screening test? |
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Definition
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Term
| What measure answers the question "If I don't have the disease, what is the likelihood that I will test negative?" |
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Definition
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Term
| How is sensitivity of a test found? |
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Definition
a / a + c
those that test positive divided by all with the disease |
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Term
| How is the validity of a test found? |
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Definition
d / b + d
those that test negative divided by all without the disease |
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Term
What is the fundamental principle of diagnostic testing?
(Not realistic) |
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Definition
| A person with a disease is different from a person without a disease and that screening (or diagnostic) tests can successfully differentiate between the two groups |
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Term
| What is true about the difference of diseased and disease-free individual's results on screening tests? |
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Definition
| Their results overlap, so there are false positives and false negatives. |
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Term
| If a screen test uses 100% sensitivity (so all false negatives are elimated), what negative effect results? |
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Definition
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Term
| If a screening test uses 100% specifity (so all false postives are elimated), what negative effect occurs? |
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Definition
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Term
| What factors are important when evaluating screening programs? |
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Definition
1. Feasibility measures
2. Effectiveness measures |
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Term
| What are the two feasibility measures? |
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Definition
1. Predictive value of a positive test (PV+)
2. Predictive value of a negative test (PV-) |
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Term
| What is predictive value of a positive test (PV+)? |
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Definition
PV+ = a / a + b
Number who test positive with disease / number with positive results
measure of yeild (ability to predict disease)
want 100% |
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Term
| What is predictive value of a negative (PV-)? |
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Definition
PV- = d / c + d
Number who test negative without disease / number with negative results
ability to correctly predict not having a disease
want 100% |
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Term
| What causes a good PV value? |
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Definition
| High sensitivity, specificity, and disease prevalence |
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Term
| What are the three types of bias when evaluating a screening program? |
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Definition
1. Volunteer bias
2. Lead-time bias
3. Length-biased sampling |
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Term
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Definition
| The people who volunteer for a screening program maybe different then the general population |
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Term
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Definition
| Lead time bais is when survival appears to increase because the disease was diagnosed early (due to screening) |
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Term
| What is length-biased sampling? |
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Definition
| Less aggressive forms of a disease are more likely to be found in a screening program because they have a longer DPCP and they usually have a better survival rate with screening |
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Term
| What is the goal of tertiary prevention? |
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Definition
| The goal is to slow or block the progression of a disease and improve the quality of life and survival among diseased individuals. |
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Term
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Definition
| a systematic error that results in an incorrect (invalid) estimate of the measure of association |
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Term
| What are the 2 effects of bias? |
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Definition
1. Bias can create spurious association when there really is none (bias away from the null)
2. Bias can mask an association when there really is one (bias towards the null) |
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Term
| What is the source of bias? |
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Definition
Primarily introduced by the investigator or study participants.
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Term
| What types of studies have bias? |
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Definition
| All study types: experimental, cohort and case-control |
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Term
| If bias occurs in design or conduct phase of a study, what can the evaluator do? |
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Definition
| The bias can be evaluated but not fixed |
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Term
| What are the two main types of bias? |
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Definition
| Selection and observation bias |
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Term
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Definition
| Selection bias is when people do not have an equal chance of being picked and that leads to a different result. |
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Term
| What type of study is most likely to have selection bias? |
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Definition
Selection bias most likely occurs with case-control or retrospective cohort studies because the exposure and outcome have already occurred at the time of study selection.
In this case the study is not independent of the exposure. |
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Term
| What are other types of bias then selection and observation? |
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Definition
Survey bias - monitoring closely find more things
publication bias - normally will not publish negative studies (that show no effect) |
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Term
| What is the result of selection bias to the odd ratio? |
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Definition
| The odds ratio is incorrect because it incorrectly represents the relationship between exposure and disease in the overall study population |
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Term
| When can selection bias occur? |
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Definition
| When the selection of exposed and unexposed subjects is not independent of the outcome. |
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Term
| What is observation bias? |
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Definition
An error that arises from systematic differences in the way information on exposure or disease is obtained from the study group.
Results in participaants who are incorrectly classified as either exposed or unexposed or as diseased or not diseased. |
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Term
| When does observation bias occur? |
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Definition
| After the subjects have entered the study |
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Term
| What are some different types of observation bias? |
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Definition
1. recall bias
2. interviewer bias
3. loss of follow-up
4. differential or non-differential misclassification |
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Term
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Definition
People with disease remember and report exposures differently than those without disease.
This results in an over- or under-estimation of association |
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Term
| How can you reduce recall bias? |
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Definition
1. Use controls who are sick
2. Use standardized questionnaires
3. Blind subjects to study hypothesis |
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Term
| What is interviewer bias? |
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Definition
| Systematic difference in soliciting, recording, interpreting information |
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Term
| When does interviewer bias occur? |
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Definition
1. When exposure information is sought and outcome is known (in case-control)
2. When outcome information is sought and exposure is known (in cohort study) |
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Term
| How can you reduce interviewer bias? |
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Definition
1. mask interviewers of study hypothesis and disease or exposure?
2. Use standardized questionnaires or methods of outcome ascertainment |
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Term
| How can you reduce loss of follow-up? |
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Definition
| You must achieve high and equal rates of follow-up for the exposed and unexposed groups |
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Term
| What is misclassification and what are the two types? |
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Definition
Misclassification is if a subject's exposure or disease is classified incorrectly.
The two types are non-differential and differential |
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Term
| What are non-differential misclassification |
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Definition
1. If incorrect with respect to disease classification are independent of exposure
2. If incorrect with respect to exposure are independent of disease
Moves towards the null making groups more similar |
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Term
| What are differential misclassification? |
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Definition
Occurs when the amount of misclassification differs between groups being compared.
Can occur when information is colledted differently from each study group |
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Term
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Definition
An alternative explanation for observed association between an exposure and disease.
A mixing of effects. Another factor that is associated with the disease distorts the association between exposure and disease. |
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Term
| What is the result of confounding? |
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Definition
| To distort the true relationship toward the null (negative confounding)or away from the null (positive confounding) |
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Term
| What is the criteria for a characteristic to be a confounder? |
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Definition
It must have a relation to both the disease (outcome) and the exposure under study
It can be a risk factor, preventive or correlate for a cause of disease (like ses)
Must be associated with disease independently of exposure. |
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Term
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Definition
If characteristic is associated with disease, then risk of disease is different among people with the characteristic compared to those without
If characteristic is associated with exposure, then the distribution of the characteristic is different among people with the exposure compared to people without exposure. |
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Term
| How do you measure confounding? |
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Definition
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Term
| How do you determine of there is confounding? |
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Definition
1. Determine the strength of the association between the confounder and the disease is evaluated.
2. Is the confounder present among both exposed and unexposed individuals.
3. Determine if there is an association between between the confounder and the exposure. |
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Term
| When can you control for confounding? |
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Definition
| design and analysis phase |
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Term
| What is necessary to control for confounding? |
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Definition
| You must have information on variables that are potential confounders |
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Term
| What are the three methods of controlling confounding in the design phase? |
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Definition
1. randomization
2. restriction
3. matching |
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Term
| How does randomization control confounding and when is it successful? |
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Definition
Randomization ensures that the treatment assignment occurs in an unbiased fashion and without guarantee control for unknown confounders.
Only can be used in experimental studies |
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Term
| What is restriction to control for confounding? |
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Definition
| restriction means that admissibility criteria for study subjects are limited. For example, small age ranges and limit to one gender. |
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Term
| What are the advantages and disadvantages of restriction? |
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Definition
Advantages - simplicity, convenience, low expense, and effectiveness
Disadvantages - difficult to find enough study subjects and limits the generalizability of the study |
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Term
| What is matching confounders? |
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Definition
| the process of making a study group and a comparison group comparable in potential confounders (used in cohort and case-control studies) |
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Term
| What are the advantages and disadvantages of matching confounders? |
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Definition
Advantages - for small studies in case-control and for complex nominal variable (like occupation)
Disadvantages - not possible to study matched factors, difficult and expensive to match, and it is possible to overmatch |
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Term
| What are the three methods to control for confounding during analyses phase? |
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Definition
1. standardization
2. stratification
3. multivariate methods |
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Term
| What is standardization and when is it used? |
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Definition
Standardization weights averages of the relative risks
Used to control for demographic variables like age, race and gender.
Should only be used if stratum-specific estimates are similar to one another |
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Term
| What is stratification and when is it used? |
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Definition
It is the process of or result of separating a sample into several subsamples according to specified criteria.
Stratification is always done to evaluate for confounding but it does not allow investigators to control simultaneously for many variables |
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Term
| What is multivariate analysis and what are the disadvantages? |
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Definition
Multivariate analysis is a mathematical model that describes the association between exposure, disease, and confounders.
Using any multivariate model requires the data to be compatiable with the model's assumptions. |
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Term
| What is residual confounding? |
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Definition
| confounding that remains even after many confounding variables have been controlled |
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Term
| What are the two main types of epidemiologic study design? |
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Definition
1. Descriptive
2. Analytic |
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Term
| What are the two main types of analytic testing? and which is most common? |
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Definition
1. Experimental with randomized and non-randomized trials
2. Observational including cohort, case-control, and cross-sectional
90% of experimental studies are observational |
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Term
| What are the keys points of a descriptive study? |
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Definition
1. Do not test hypothesis but generate questions
2. Focus on patterns of disease by person, place, and time.
3. Usually have no comparison group
4. answer no why questions |
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Term
| What are the key points of analytic study? |
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Definition
1. Test a hypothesis
2. Include a control or comparison group
3. Has a more complex design than a descriptive study |
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Term
| What are the key points of observational design studies? |
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Definition
1. Study observes what has occurred naturally
2. Investigator does not manipulate exposure status of study participants
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Term
| What are the key points of experimental design studies? |
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Definition
1. Investigator manipulates the exposure
2. Equivalent as possible to a laboratory experiment
3. The best way to establish causality |
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Term
| Name 5 types of descriptive studies. |
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Definition
1. case reports
2. case series
3. survelliance
4. ecological
5. descriptive surveys |
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Term
| Describe a ecological study |
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Definition
1. study of group characteristics not individuals
2. correlation between disease rates and exposures are based upon average exposure levels and average disease rates.
3. These studies have comparison group but NO data on individual exposures |
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Term
| What are the advantages of ecological studies? |
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Definition
1. availability of data on exposures and disease
2. can be done quickly and with limited resources
3. Exposures may differ substantially between cities, states, and countries
4. Analysis in fairly simple
5. Used to get hypothesis |
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Term
| What are limitations of ecological studies? |
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Definition
1.Many biases and limitations
2. Are more suseptible to confounding than individual risk studies
3. Can't determine whether exposure preceded the outcome
4. Subject to "ecological fallacy" |
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Term
| What is ecological fallacy |
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Definition
| It is tributing corelation when none exists because what occurs at the group level does not hold true for individuals |
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Term
| What is a cross-sectional study? |
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Definition
| A descriptive or analytical study that looks at the prevalence of disease and/or exposure at one point in time classifying them as diseased or non-diseased, and exposed or unexposed |
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Term
| What populations are identified for cross-sectional studies? |
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Definition
1. When you want to identify risk factors
2. when you know the population has some risk factors and would like to explore the associations with disease
3. you don't usually know the exposure and disease status of individuals of the population |
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Term
| What types of analysis occur on cross-sectional studies? |
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Definition
1. exposure-odds ratio (odds of exposure among diseased compared to non-diseased
2. disease-odds ratio (odds of disease among exposed compared to unexposed
3. prevalence odds ratio (estimates the incidence rate ratio if factor occurs over extended period of time and the duration of the outcome is not affected by exposure status) |
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Term
| How is prevalence odds ratio (POR) found? What does it estimate and when is it best? |
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Definition
ad / bc
estimates incidence rate ratio
best for cross-sectional studies of chronic diseases |
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Term
| When is prevalence ratio used and what does it estimate? |
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Definition
Prevalence ratio (PR) is used when outcome occurs over a shorter time period
It estimates cumulative incidence ration (CIR) |
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Term
| What are the advantages of a cross-sectional study? |
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Definition
1. Quicker and cheaper than cohort
2. Useful to study morbidity or pre-diagnoses
3. Collect detailed data on exposers adn confounders
4. Do not have to know disease/exposure status before study |
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Term
| What are the limitations of a cross-sectional study? |
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Definition
1. Problem with selection bias esp. diseases with long duration (survival bias), loss of follow-up, volunteer bias
2. Patience history is the only way to determine time sequence between exposure and disease
3. Rely on subjective information |
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Term
|
Definition
1. Samples a population and cases of disease are identified and enrolled
2. Control group is identified and enrolled for the same population
3. Exposures are determined for individuals in each group |
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Term
| Different types of case-control studies |
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Definition
1. Community-Based (population-based)
a. prevalence case-control study
b. incidence case-control study
2. Cohort-Based (nested) - review
3. Case-Crossover Study - review |
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Term
| When is it desirable to conduct a case-control study? |
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Definition
1. when exposure data are exprensive or difficult to obtain
2. When a disease has a long induction and latent period
3. When the disease is rare
4. When there is little information about the disease
5. When population is dynamic |
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Term
| Why is it impossible to find rates for case-control studies? |
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Definition
| You do not know the denominator (the total population) |
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Term
| What are the controls for the case control study and why are controls important? |
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Definition
A. A sample of the source population that gave rise to the cases
B. To estimate the exposure distribution in the source population that produced the cases (becomes the denominator) |
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Term
| How are general population controls selected? |
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Definition
Normally from the same geographic population, with random digit dialing, residence lists, etc.
Control confounding by matching gender and age |
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Term
| What are the advantages of hospital controls? |
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Definition
1. Less expensive
2. More cooperation and easy to find
3. Recall is often better |
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Term
| What is a proxy respondent? |
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Definition
| Answers case-control study questions when the case is deceased or unavailable |
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Term
| How does "nested" case-control studies minimize control selection biases? |
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Definition
| Controls come from same population as cases |
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Term
| How do you conduct a nested case-control study? |
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Definition
1. performed after cohort study
2. choose all cases of disease among cohort
3. Identify controls among cohort without disease
4. Obtain information on exposures and potential confounders
5. Compare prevalence of exposure between cases and controls |
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Term
| What are case-crossover studies? |
|
Definition
1. A variation of case-control study
2. Useful design in studying risks which are only briefly increased following exposure
3. Requires fewer subjects and minimizes selection baises, and confounding
4. Exposure frequency during hazard period is compared with that in same case during a control period |
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Term
|
Definition
| A period of increased risk following exposure. This is the time period studied in a case-crossover study |
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Term
| What is a would criterion? |
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Definition
When selecting a control group consider if a member of the control group had in disease, WOULD that person be in your study?
ONLY yes is acceptable controls |
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Term
| In case-control studies cumulative incidence or incidence rate of a disease is not possible to calculate. What is used instead? |
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Definition
| Odds ratio - which is the ratio of the probability of an even occurring to the probability of it not occurring |
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Term
| How do you find odd ratio? |
|
Definition
Odds ratio = odds of an exposed person being a case / odds of unexposed person being a case
formula = ad / bc |
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Term
| When is odds ratio a good estimate of relative risk? |
|
Definition
1. controls are representative of individuals in base population
2. cases are representative of all individuals with the disease of interest in the base population
3. the disease is relatively rare |
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Term
| The leading cause of death worldwide is: |
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Definition
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Term
| What are the main causes of HIV transmission around the world |
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Definition
Africa - hetreosexual transmission
Asia - IDU in urban and plasma in rural
Eastern Europe - IDU
West - MSM and IDU |
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Term
| What is the largest contribution to the deciline of most infectious disease? |
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Definition
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Term
| 5. What causes the “emergence” of a new Infectious Disease? |
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Definition
a. Population Growth
b. Change in the underlying health of the community (other infections, starvation, etc.)
c. Speed of travel
d. Geographic alterations (homes, dams, forests, etc.)
e. Climate changes
f. War and social disruption
g. Changing living patterns
h. Medical advances |
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Term
| What is attack rate and how does it compare to incidence? |
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Definition
Number of cases per number of individuals exposed
This concept is the same as incidence if all cases are new cases and all to the base population is exposed. |
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Term
| What is Secondary Attack Rate |
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Definition
Number of cases per individuals exposed to initial cases
This becomes an important measure of the efficiency of Person to Person transmission |
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Term
| What is generation period? |
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Definition
| Interval from infection of the host to maximal infectivity of that host for others (“shedding” of infectious agent) |
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Term
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Definition
| Protection of an entire population (immune and non-immune) from infection brought about by the presence of a “sufficient” number of immune individuals to prevent person to person transmission from occurring (reducing number of “susceptibles”) |
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Term
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Definition
| Ability of agent to invade and multiply in a host |
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Term
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Definition
| The ability of a pathogen to produce a clinically apparent illness in a host |
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Term
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Definition
| Ability of agent to produce severe disease in a host |
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Term
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Definition
| Ability of agent to produce immune response in a host |
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Term
| How are infectious agents classified |
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Definition
1. Microbiologic (viral, bacterial, fungal, etc.,.)
2. Mode of Transmission (generation, contact, vehicle, source)
3. Pathogenic Mechanism (gastrointestinal, respiratory, hemorrhagic fever, etc.,.)
4. Reservoir of the organism (human, animal, soil, water) |
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