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Continuous Outcomes

Groups Purpose Conditions or Assumptions Test Descriptive Measures (also used to calculate CIs)

Single sample

Compare mean to historical or hypothetical (known) mean

Standard deviation known or N large and approximate normality

One-sample z-test

Mean, std deviation, difference from historical mean

 

Compare mean to historical or hypothetical (known) mean

Standard deviation unknown; approximate normality

One-sample t-test

Mean, std deviation, difference from historical mean

Two independent samples

Compare means

Approximate normality

Two-sample t-test

Means, std deviations, pooled std deviation, difference in means

 

Compare medians (Pr (X < Y))

Use for highly non-normal outcomes

Wilcoxon rank-sum test Mann-Whitney U test

Medians, quartiles, difference between medians

Two+ independent samples

Compare means (any or overall difference)

Approximate normality

Analysis of variance (ANOVA)

Means, std deviations, pairwise differences in means

 

Compare medians (outcome distributions)

Use for highly non-normal outcomes

Kruskal-Wallis test

Medians, quartiles, pairwise differences in medians

Matched Pairs (2)

Evaluate whether mean of differences nonzero

Approximate normality

Paired t-test

Mean of differences, std deviation of differences

 

Evaluate whether median of differences nonzero

Use for highly non-normal outcomes

Wilcoxon sign-rank test

Median of differences, quartiles of differences

Matched Sets (> 2)

Evaluate whether mean of differences nonzero

Approximate normality

Repeated measures ANOVA

Mean of differences, std deviation of differences

 

Evaluate whether median of differences nonzero

Use for highly non-normal outcomes

Friedman test

Median of differences, quartiles of differences

 

 

 

rev. 29-Aug-2016

 

 

 

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