Table 1.
Method | Strengths | Weaknesses |
---|---|---|
Restriction | Easy to do, easy to understand | Can limit power |
Matching | Easy to do, easy to understand | Difficult to match on a large number of variables |
Stratification | More powerful than restriction and matching | Difficult to deal with strata with small numbers. Can introduce residual confounding if subjects with very different values of a factor are grouped into a strata (eg, quartiles) |
Multivariable regression | More powerful than restriction and matching | Model building can be complicated Can introduce residual confounding if subjects with very different values of a factor are grouped into a strata (eg, quartiles) |
Propensity scores | Can be used to assess amount of unmeasured confounding that exists | Not designed specifically to deal with unmeasured confounding |
Instrumental variables | One of the newer, more powerful methods | Difficulty in finding the optimal instrumental variable |
a All methods cannot control for unmeasured confounding.