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Flashcards in Epi Class 6 Deck (21):

experimental study

assigns participants to intervention and control groups in order to examine whether an intervention causes an intended outcome.

• Because the researcher assigns participants to receive a particular exposure, the exact timing, dose, duration, and frequency of the exposure are known.

• Considered to be the “gold standard” in epidemiology FOR CAUSALITY


Types of experimental study

– Clinical trials: evaluate treatment for ill people

– Field trials: evaluate interventions for disease prevention (like vaccine trials)

– Community trials: evaluate community-wide interventions (like fluoridation of public water supplies)


randomized controlled trial (RCT

• Some participants are randomly assigned to an active intervention group

• The remaining participants are assigned to a control group

• All participants from both groups are followed forward in time to see who has a favorable outcome and who does not


superiority trials

Aim to demonstrate that a new intervention is “better” than some type of control

• Because the term “better” can be defined in so many ways, the researcher must carefully define what constitutes a favorable outcome for the experiment


equivalence trials

is the new intervention as good as the comparison one?


non-inferiority trials

is the new intervention no worse than the comparison one?



experimental research should be conducted only when there is genuine uncertainty about which treatment will work better


Distributive justice

the source population must be an appropriate and non-exploitative one


Beneficence and nonmaleficence

Beneficence = do good
Nonmaleficence = do not harm

researchers must balance the likely benefits and risks of the study


Respect for persons

– Participants must volunteer for a study of their own volition (autonomy) without being unduly influenced by the prospect of being compensated for their participation

– Participants must be able to understand what it means to be a research subject, including the possibility of being assigned to a control group instead of the new intervention

– Potential participants must be given enough information to give their own informed consent

– Researchers must protect the safety and privacy of participants



The proportion of individuals in the control group who experience an unfavorable outcome who could have been expected to have a favorable outcome had they been in the active group instead

(the term efficacy is used for a highly-monitored, in-a-perfect-world study. Effectiveness is used for a real-world, not-perfect study)

• A high efficacy is an indicator that an intervention is successful.

• Efficacy (effectiveness) is very similar to AR%

• “__% of the people in the control group could have prevented their bad outcome if they had been in the intervention group instead”


Number needed to treat (NNT)

the expected number of people who would have to receive a treatment to prevent an unfavorable outcome in one person (or, alternately stated, to achieve a favorable outcome in one person)

• A small NNT indicates a more effective intervention.

• If a drug is intended to prevent stroke and has an NNT of 5, then 5 people have to take the drug for one year (or some other specified time period) to prevent one of the 5 from having a stroke.

• If a drug has an NNT of 102, it means that 102 people have to take the drug to prevent one of the 102 from having a stroke.



Rate in intervention group

a / (a + b)



Rate in control group

c/ (c + d)


Efficacy formula

(Rc - Ri) / Rc


NNT formula

1 / (Rc - Ri)


Analytic Frameworks: Treatment-received approach

limit analysis to the participants who were fully compliant with their assigned intervention [efficacy = laboratory setting]



not all participants will follow the protocol


Placebo effect

even a placebo will make many patients feel better


Loss to follow-up

even if the same % of people in each treatment group are lost to follow-up, there may be bias (the treatment group may quit because they get healthier and the placebo group may quit because they get sicker)


Analytic Frameworks: Treatment-assigned approach

intention-to-treat approach

includes all participants even if they were not fully compliant with their assigned intervention [effectiveness = real world setting]