Measures of Association Flashcards
Sensitivity
The ability of a test to identify correctly those who have the disease
Proportion of diseased people who are correctly identified as “positive” by a test
TP/(TP+FN)
100-%sensitivity=%false negative
Specificity
The ability of a test to identify correctly those who do not have the disease
Proportion of non-diseased people who are correctly identified as “negative” by a test
TN/(TN+FP)
100-%specificity = % false positive
Morbidity
Rate of disease in a population
Can be described by cumulative incidence proportion, incidence rate, prevalence, attack rate
Cumulative incidence proportion
Period of time during which all of the individuals in a proportion are considered to be at risk for the outcome
Measure of risk
Incidence rate
Number of new cases of a disease that occur during a specified period of time in a population at risk for developing the disease
Measure of morbidity
Incidence rate per 1000
New cases/those at risk x 1000
Prevalence
Number of affected persons present in the population at a specific time divided by the number of persons in the population at the time
Measure of morbidity
Attack rate
The number of people exposed to something and get the associated outcome divided by the total number of people exposed
Measure of morbidity
Mortality rate
Number of deaths from a cause in a certain population over a specific period of time
Standardization
Set of techniques used to remove the effects of differences when comparing two or more populations
Direct standardization
Rate of death/disease that would have been observed in the study population if it had the same age distribution as in the standard population
Indirect standardization
Compares the rate of death/disease observed in the population to the expected rate from the standard population
Risk Ratio
Ratio of the risk of disease in exposed individuals to the risk of the disease in unexposed individuals
a/(a+b) / c/(c+d)
Odds Ratio
The ratio of the probability of occurrence of an event to that of non-occurrence
(a x d) / (b x c)
When are risk ratios used
Prospective, cohort studies
When are odds ratios used
Retrospective, case control studies
Attributable risk
The amount or proportion of disease incidence or risk that can be attributed to a specific exposure
AR = Risk exposed - risk unexposed
Population attributable risk
The attributable risk of an entire population whether or not all in the population have direct exposure
Hazard Ratio
The rate at which an unfavorable event occurs; commonly used in survival analysis
Confidence interval
Numerical range used to describe how reliably study results reflect the entire population
Number needed to treat
Number of patients who would have to receive the treatment for one of them to benefit
Number needed to harm
Number of patients who receive a treatment before one adverse event occurs
Confidence interval interpretation
General interpretation statement: It is likely that the true mean difference between the two groups is somewhere between the first number in the range and the second number in the range
