Lecture 10 (RCTs) Flashcards Preview

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Flashcards in Lecture 10 (RCTs) Deck (18):
1

RCT (def)

-Subjects randomly allocated to treatment or comparison grp, followed to compare outcomes

2

Omenn et al: Beta C and Vit A on lung cancer/cardiovasc disease (CARET)

-Conclusion: didn't reduce risk, may have increased it
-Don't know which one though

3

Alternatives to randomization in exp study

-Historical comp grp
-Non-randomized concurrent comp grp ( systematic allocation or matching)

4

Systematic allocation in exp study

-Allocation according to predetermined rule
-Can --> diffs in confounders even w/o manipulation

5

Matching in exp study

-Selection such that grps are similar w/respect to potential confounders
-Doesn't work for unknown confounders (validity of study depends on this)

6

Randomization

-Allocation by chance (each has fixed prob, can't be predicted)
-Pros: no selection bias, defends against confounding w/large n
-Can also be stratified randomization

7

Blinding (purpose)

-Prevents info bias --> diff misclassification
-More subjective the outcome, more important

8

Benefits of placebo

-Blinds participants and researchers
-Psych benefits
-Helps keep participants assigned to comp grp

9

2x2 factorial design

-Evaluates 2 diff treatments in single study
-n needed = considerably smaller

10

Avoiding effect mod in 2x2 factorial design

-Treatments have independent mechanisms of action
-Treatments act on 2 separate outcomes

11

Albanes et al: a-tocopherol, beta C on lung cancer

-Double blind, placebo
-Baseline: very similar characteristics
-Conclusions: neither reduced risk, Beta C may have ^ it (stopped before end)

12

Crossover design (RCT)

-Upon completion, switched to other treatment
-Each patient serves as own control

13

What does non-adherence do in crossover design

-Biases estimate towards Ho (no effect)

14

Adherence in CARET

-15-20% of certain grps stopped, probably --> underestimation of effect

15

Run-in period

Prior to randomization, assessing adherence to determine who will be included
-Increases prob that subjects will adhere

16

Number needed to treat

# of patients that would need to be treated to prevent one adverse outcome

17

Summary of pros of RCTs

-Investigator controls stuff
-Randomization eliminates selection bias and reduces likelihood of confounding
-Blinding eliminates info bias --> diff misclassification

18

Summary of limitations of RCTs

-Can't be used for harmful exposures
-Often insufficient # of subjects (reluctant, eligibility criteria = restrictive)
-Expensive