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Matching

The aim of matching is remove confounding by matching subjects to be similar on a potential confounder. Doing so eliminates (or reduces) confounding, as well as reducing variability thereby increasing power.

Recall a paired t-test with two independent samples:
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with n-1 degrees of freedom and standard error:
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The test is inversely related to variance.

Types of Matching

  • Matched Pairs (covered today)
  • Categorical Matching (unmatched analysis, stratified or regression)
    • Stratify cases, then find equal number of controls for each category (or equal multiple).
  • Caliper Matching
    • Only for continuous variables
    • Similar to categorical but not the same
  • Nearest Neighbor
    • Select 'closest' control as match
    • May have minimum match criteria

Matching in Follow-Up Study

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Remove Confounding (C) in the study sample between Exposed (E) and unexposed by matching on the potential confounders.

There are 4 possible combinations of outcomes in exposed and unexposed groups:
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Corncordant pairs have the same outcome between pairs, and opposite in discordant pairs.

An example presentation for matching 2x2 tables:
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Notice the column and cell totals now equal the value of cells a,b,c,and d in the original table.

Matching in Case-Control Study

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Remove CofoundingConfounding (C) in the sample study between cases and controls by matching on potential confounders where for each case we select a control with the same values for the confounding variables.

 

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