Epidemiology Flashcards
what is validity?
accuracy - does it correspond to what is true
what is reliability ?
precision - does it give consistent results when repeated
(reliability/validity):
1. sensitivity
2. specificity
3. likelihood ratios
all three are part of validity
what is the gold standard? (2)
- The method that would ideally give 100% correct results
- Does not exist, we use the best test available
what is pre-test probability?
probability of having the disease BEFORE testing
what is post-test probability?
probability of disease AFTER test result
are the pre-test and post-test probabilities low or high for:
1. a positive test
2. a negative test
- pre-test: low, post-test: high
- pre-test: high, post-test: low
what is a true positive?
positive test + disease positive
what is a false negative?
negative test + disease positive
what is a true negative?
negative test + disease negative
what is a false positive?
positive test + disease negative
what is sensitivity? how do we calculate it?
- true positive rate (positive test +disease positive)
- proportion of patients with disease who test positive
- TP / TP +FN (denominator is everyone who is disease positive, regardless of test result)
what is specificity? how do we calculate it?
- true negative rate (negative test + disease negative)
- proportion of patients without the disease who test negative
- TN / TN + FP (denominator is everyone who was disease negative, regardless of test result)
what is the predictive value of a positive test? how do we calculate it?
- proportion of patients with positive tests who have the disease
- TP / TP + FP (denominator is people with positive test, regardless of disease presence)
what is the predictive value of a negative test? how do we calculate it?
- proportion of patients with negative tests who don’t have the disease
- TN / TN + FN (denominator is people with negative test, regardless of disease presence)
T/F: sensitivity and specificity change with prevalence and incidence.
FALSE: they are fixed characteristics
T/F: PPV and NPV change with prevalence and incidence.
TRUE
As prevalence increases, (increase/decrease)
1. PPV ____
2. NPV ___
- increase
- decrease
what do we need to consider when determining pretest probability? (3)
- Prevalence of disease
- Characteristics of patient pool
- Info about the patient
what is the receiver operating characteristic curve and what do we want it to look like?
- shows what happens to sensitivity and specificity as different cutoffs are being used
- want curve to be closer to 1 (means test is more accurate)
what is epidemiology? (2)
- the study of disease occurrence in human populations
- the study of distribution and determinants of disease frequency
Describe the Grand Experiment (3)
- John Snow thought cholera was reproduced in the body and spread through water/food
- compared 3 districts that had different water companies (randomized)
- statistical association between water company (contamination level) and death from cholera
what are the two types of epidemiology?
- descriptive epidemiology
- analytical epidemiology
what is descriptive epidemiology? (2)
- distribution of disease in population
- description in terms of person, time and place
what is analytic epidemiology?
- examine hypothesized causal relationship
- identify or measure effect of risk factors or health effect of specific exposure
what were the 3 high impact studies in epidemiology?
- framingham heart study: equations for CVD risk
- British doctors study: link between smoking and cancer
- Nurses’ health study: risk factors for chronic diseases in women
what are the 5 D’s (outcomes of disease)?
- death: bad outcome (mortality)
- disease (symptoms, signs, abnormalities - morbidity)
- discomfort
- disability
- dissatisfaction
what is the 6th destitution?
financial cost of illness (for individuals or society)
what are the main epidemiological tools? (6)
- vital statistics (mortality)
- disease registries
- notifiable disease
- administrative systems
- special surveillance systems
- community assessments
what is prevalence and how do we calculate it?
- proportion of persons in population who have a disease at a specific time point
- cases / total population
T/F: point prevalence and prevalence are two different things
FALSE
what is incidence?
quantifies nb of new cases of disease that develop in population AT RISK during specified interval
what are the two types of incidence measures?
- cumulative incidence (incidence proportion)
- incidence rate (incidence density)
T/F: when calculating incidence of endometrial cancer (uterus), we include men and women
FALSE: only women are at risk since only they have a uterus!!
what is cumulative incidence (incidence proportion)? how do we calculate it?
- proportion of individuals initially free of the disease who develop it during a time period
- nb new cases / population at risk
T/F: cumulative incidence is the probability or risk of developing a disease
TRUE
what is incidence rate (density) and how do we calculate it?
- nb of events divided by the amount of person-time observation
- new cases / total person-time of observation
T/F: incidence rate measures how quickly people are developing a disease
T/F: incidence rate is the TRUE rate because it measures number of cases per unit time
TRUE for both
how are prevalence and incidence rate related?
prevalence = incidence rate x duration
what are the special types of incidence measures? (2)
- mortality rate
- attack rate (cumulative incidence)
when are prevalence and incidence most helpful?
- prevalence is most useful for health care providers (assess public health impact)
- incidence is most useful to assess exposure disease relationship and risk factors
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