more exam 2 prep

formula for point prevalence

existing cases / total population x 100%

formula for incidence rate

new cases during the period / person-time at risk

formula for incidence risk

new cases during the period / population at risk at the start

formula for standard infection ratio

observed infections / predicted infections

interpret prevalence

existing cases during a specific period

interpret incidence

new cases during a specific period

interpret incidence risk

the probability of developing a disease during a specific period

interpret incidence rate

the speed at which new cases occur per person time

forumla for odds ratio

exposure odds among cases / exposure odds among controls

forumla for exposure odds

number of previous exposed / number of unexposed

formula for rate difference

rate in exposed - rate in unexposed

formula for rate ratio

rate in exposed / rate in unexposed

forumla for risk ratio

risk in exposed / risk in unexposed

how is a cross-sectional study grouped

exposure AND outcome, all from the same population

limit of a cross-sectional study

cannot determine if exposure or outcome occurred first because they are measured at the same time

what are common measures for cross-sectional studies

point prevalence

existing cases / total pop x 100%

how is a cohort study grouped

by exposure

limits of cohort study

groups can differ in age, underlying conditions, etc.

common measures of a cohort study

incidence risk

number of new cases / population at risk at start

how are case-control studies grouped

by outcome

limits of case-control studies

hard to select proper controls, or controls are inaccurate

common measures for case-control studies

• odds ratio

  • exposure odds among cases / exposure odds among controls

• exposure odds

  • # previously exposed / # unexposed

how are RCTs grouped?

by assigned exposure

common measures of RCTs

• incidence risk

  • new cases during period / person-time at risk

• incidence rate

  • new cases during period / person-time at risk