EBP: Cohort study

Experimental studies/ intervention

Phase 1,2,3,4

drug development and drug approval

Observational studies

descriptive studies e.g. case reports, case series

secular trend analysis: look at how disease trends change over time

cross-sectional studies

drug utilisation

Analytical studies

cohort studies: cohort, large simple, registries

case control studies

examples of under representative patient groups

women, pregnant

children

alcoholics

What is an observational study

Non-experimental

No risk to patients

No control over exposures assigned but can select subjects

Cohort study

Recruit people in a population without the disease (without the disease of interest)

collect exposure information (some people do, some don’t)

collect information on incident outcome

Follow up

analysis is split into exposed vs not exposed

Find risk ratio: exposed/unexposed

What does exposure mean

exposure of interest

e.g. alcohol intake some don’t drink, some drink more in different seasons

misclassification may lead to underestimate or overestimate

Outcomes design

• outcome of interest needs to be clearly defined

• length of follow up

• how many years do we run the study

• what about people lost to follow up, bias

Misclassification

Non-differential: to the same degree for all groups

Differential: misclassification applied to one group

misclassification of the wrong patient group

What are covariates

• other variables that may influence the results of the study e.g.

• age

• gender

• other diagnoses

• other medication

• smoking, BMI, socioeconomic status

What is confounding

an external factor than can influence the variables in the study

can lead to bias

have to evenly distribute population

Channelling

a type of selection bias that occurs when patients with different prognoses or risk factors are disproportionately assigned to different treatments within a study

How can we control confounding

• randomisation : even distribution

• restriction

• matching: match exposure vs non-exposed group

• Stratified analysis

• multivariate analysis: –Takes into account a number of factors simultaneously