Class 11-12: Confounding

Question 1

Counterfactual theory

Answer 1

Counterfactual outcomes based on individuals most similar to test subjects..but can’t take back the exposure so you can’t use same person to test effects of an exposure. So, you try to compare to a subject you can exchange w/. This subject.

Question 2

Exchangeability

Answer 2

Comparability

Question 3

Lack of exchangeability

Answer 3

Confounding

Question 4

3 aspects of evaluating internal validity of study

Answer 4

Confounding or effect modification
Bias
Statistical significance

Watch CBS before claiming internal validity

Question 5

Confounding variable

Answer 5

A 3rd variable that distorts an asso. Btw exposure and outcome- makes groups NOT exchangeable in terms of asso.

Question 6

Direct Acyclic Graph

Answer 6

Exposure------>Outcome
               ^.              ^
                I.              I
                I               I
              Confounder

Question 7

Other ways to define confounding

Answer 7

A mixing of effects; an asso. Distorted d/t them (exp. and outcome) being mixed.

Confounding is a confusion of effects. Exp. is distorted b.c the effect of a 3rd factor is mistaken for effect of exposure

Question 8

3 requirements of con founders

Answer 8

1. Asso. w/ Exposure
2. Asso. w/ outcome
3. Not directly in the causal-pathway linking exposure to outcome

Question 9

How test for confounding [3 steps]:

Answer 9

1-calculate crude outcome measure (OR/RR)-unadjusted asso.
2-Calculate outcome measure of asso. (OR/RR)- for all layers of the 3rd variable
3- Compare [divide by difference of unadjusted & adjusted the unadjusted vs. adjusted measures of outcome: if >15% confounding is present

Question 10

2 main impacts of confounders:

Answer 10

1-Magnitude of asso.

2-direction of asso.

Question 11

What must be included in the adjusted OR

Answer 11

Must state what was accounted for in the adjustments

Question 12

Purpose for controlling for confounders:

Answer 12

To get more precise estimate of the measure of asso.

Question 13

Ways to control for confounding:

Answer 13

• study design stage[during study]

- Analysis of data stage [after research completed]

Question 14

3 study design stage [during research]: ways to control for confounding

Answer 14

Randomization, restriction, and matching

Question 15

2 study design stage [after research]: ways to control for confounding

Answer 15

Stratification (w/ weighting)

Multivariate statistical analysis [regression analyses]

Question 16

Randomization

Answer 16

HOPEFULLY Allocates an equal # of subjects w/ the known confounders into each intervention grp.

Not for sure..only can be used for interventional studies

Ex: hoping–flipping a coin

Question 17

Restriction

Answer 17

Don’t allow certain subjects to control for confounders….doesn’t effect internal validity but it can effect EXTERNAL validity (generalizability)

Question 18

MAtching

Answer 18

Study subjects in matched pairs r/t confounding variable to equally distribute confounder among study group.

Difficult to accomplish/time consuming. Can over match…not control for other factors besides the confounder.

Question 19

Stratification

Answer 19

Descriptive and statistical data analysis between exposure and outcome…ex: 2x2 table young vs. old

This can be impractical

Question 20

Multivariate analysis

Answer 20

This is the most common: Statistical analysis of data by mathematically factoring efforts of the confounding variable…ex: crude vs. adjusted

Time consuming.

Question 21

Effect modification

Answer 21

A 3rd variable that modifies the magnitude of effect of a true asso. By varying it w/in different levels of a 3rd variable-modifies the effect across the strata

Question 22

What’s the different about effect modification and confounding?

Answer 22

An effect modifying variable should be described and reported at each level of the variable….rather than controlled for

Question 23

Ex of effect modification in class: live birth weight and mortality:

Answer 23

Unadjusted OR:1.06
Adjusted OR:1.02
=
No confounding present, BUT
When looking at strata layers of birth weights...the mortality OR varied greatly

Question 24

Steps for testing Effect modification:

Answer 24

1: Calculate crude measure of asso. Btw exposure and outcome
2: Calculate measure asso. Btw exposure and outcome for each strata
3: Compare each of the stratum-specific measures of asso. [OR] btw each other while referencing adjusted measure….>15% = effect modification present

Question 25

Is a vital detail that we want to describe w/in a study.

Answer 25

Effect modification