E-modules ons measures of association and public health impact

8 important questions on E-modules ons measures of association and public health impact

Effect measure modification

Present if association differ across levels of a third factor

- het geldt alleen voor jou data, bv in een ander land kan het anders zijn (genen, cultuur etc)

Interviewer / observer bias =

Collection of data is deferent for cases and controls because the disease status is known to the interviewer:

  • exposure status is differently interpreted by interviewer
  • interviewer elicits exposure status differently


e.g. Smoking behavior in lung cancer cases

Two types of validity

Internval validity
  • that you are measuring in your cohurt study what you intent to measure and that this is free of bias

external validity / generazability
  • how representative is your sample can you extrapolate your result to a broader population
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Main source of selection bias cohort study:

Loss-to-follow-up / attrition

Association measures in study designs

Cross-sectional studies
  • prevalence ratio

prospective studies (trails, cohort studies)
  • relative risk (incidence rate ratio, incidence proportion ratio)

case control studies
  • odds ratio

Interpretation of ratio measures

Ratio: ranges from 0 to infinity

1 = no association between exposure and disease
>1 = positive association or increased risk
< 1 = negative association, decreased risk, or protective effect

example:
RR = 2       interpreted as twofold increase in risk
RR = 0,5    interpreted as 50% decrease in risk
OR = 1        interpreted as no association

Population attributable risk (PAR); berekenen met

Using incidence rate:
  • incidence rate in population - incidence rat in unexposed

using incidence proportion:
  • incidence proportion in population - incidence proportion in unexposed

using attributable risk and prevalence
  • AR x Pe

What are the steps of an outbreak investigation

  • Confirm outbreak and diagnosis
  • form outbreak control team
  • define a case
  • identify cases and obtain information
  • describe data by time, place, person
  • develop hypothesis (on source)
  • test hypothesis: analytical studies
  • additional studies
  • communicate results: outbreak report, publication
  • implement control measures

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