week 7: infectious disease research -

what is a study design?

a plan for selecting participants & deciding how and when to collect info & answer a research question

what is exposure? ex?

the factor being studied

• antibiotic use

• influenza vax

• injection drug use

what is outcome? ex?

the health event or condition being measured

• c diff infection

• influenza infection

• hep C infection

what is a descriptive study?

• describes disease patterns by person, place, and time

• asks how common a condition is, who, when, where are people affected

• ex) number of influenza cases by age group

what is an analytical study?

• examines associations

• is an exposure associated with an outcome?

• ex) influenza occurrence between vax and unvax groups

what is an observational study?

• researches measure exposures & outcomes without assigning the exposure

• ex) cross sectional, cohort, case-ctrl studies

  • choose antibiotic A or B during routine care, compare recovery between groups

what is an experimental study?

• researchers assign an intervention & measure outcome

• ex) RCTs

  • researchers randomly assign antibiotic A or B and compare recovery between groups

what is a cross-sectional study?

• sample is people are from a defined population

• exposure and outcome assessed during the same period

what’s a limitation of a cross-sectional study?

cannot determine if exposure or outcome came first

what are common measures in cross-sectional studies?

• point prevalence

  • proportion of people with the outcome at specific point in time

• prevalence ratio & prevalence difference

  • compare prevalence between exposure groups

what is a cohort study?

• select & group participants by exposure

• compare risk/rate of developing outcomes in a period

what’s a limitation of a cohort study?

groups can differ in age or underlying conditions, etc.

what’s a prospective cohort study?

occurs after the study begins

what’s a retrospective cohort study?

already occurred before the study begins

what are common measures of cohort studies?

• incidence risk

  • % of nurses who develop influenza during 12-wk period

• incidence rate

  • new influenza cases per 1000 person-weeks at risk

• calculate each measure w/in each vaccination group, and compare groups w/ ratio or difference

what is a case-control study?

• a defined group, classified by exposure

• researchers select participants by outcome, cases have the outcome & controls do not when selected

• controls come from the same population as cases

• researchers compare prior exposure btwn cases and controls

what is a limitation of a case-control study?

poor control selection or inaccurate exposure info can distort the results

what are common measures of case-control studies?

• cases and controls, selected by outcome

• exposure odds: number previously exposed/number unexposed, calculated separately for cases & controls

• odds ratio: exposure odds among cases/exposure odds among controls

what is a RCT?

• researchers randomly assign participants to an intervention group

• follow both groups and compare outcomes

what are common measures of an RCT?

• incidence risk

• incidence rate

how to calc prevalence ratio?

prevalence in exposed/prevalence in unexposed

how to calc prevalence difference?

prevalence in exposed - prevalence in unexposed

how to calc risk ratio?

risk in exposed / risk in unexposed

how to calc risk difference?

risk in exposed - risk in unexposed

how to calc rate ratio?

rate in exposed / rate in unexposed

how to calc rate difference?

rate in exposed - rate in unexposed

how to calculate exposure odds?

number previously exposed / number unexposed

how to calculate odds ratio (OR)?

exposure odds among cases / exposure odds among controls

what are key points of interpreting a study?

• measure association

  • risk

  • rate

  • prevalence

  • odds

• exposure

• groups

  • who’s compared

• outcome

  • what condition was measured

• time

  • when and what period

what is association? ex?

observed stat relationship between variables

ex) vax nurses had a lower influenza risk than unvax nurses

what is correlation? ex?

how two numerical variables vary together

ex) hospitals with higher staff vax coverage had lower staff influenza rates

what is causation? ex?

changing an exposure changes the likelihood of an outcome

ex) vaccination reduces influenza risk

what can be measured in a cross-sectional study?

prevalence

what can be measured in a cohort or RCT study?

risk over a specific period

incidence rate using person time

what can be measured in a case-control study?

exposure odds among cases and controls