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Statistics: ANOVA

To simplify, a one-way ANalysis Of VAriance (ANOVA) is like a t-test, but for three or more groups.

Note that t-tests and ANOVAs are applied to continuous variables (i.e., comparing sample means for variables such as age, BMI, operative time, MAP, SpO2, EBL, morphine equivalents, duty hours, ITE scores).

If the two groups are PAIRED observations (pre-op vs. post-op), then a “paired t-test” may be applied. If the three or more groups consist of REPEATED MEASURES (pre-op vs. intra-op vs. post-op vs. follow-up), then a “repeated measures ANOVA” may be applied.

Chi-square tests are applied to categorical/discrete variables (i.e., sex, obesity, diabetes, mortality, reintubation, ICU admission, board exam pass/fail). A chi-square test can be used in cases of just two groups, or in cases of three or more groups.

Other statistical tests to know include:

• Linear regression (given a set of predictors, what is the expected CONTINUOUS response).

• Logistic regression (given a set of predictors, what is the expected BINARY response).

• Mann-Whitney U-Test and Wilcoxon Signed Rank-Test (non-parametric cousins of the t-test and paired t-test, respectively).

• Fisher’s exact text (applied to the same scenarios as a chi-square test, but when the event rate is rare).


  1. Mishra P, Singh U, Pandey CM, et al. Application of student's t-test, analysis of variance, and covariance. Ann Card Anaesth. 2019;22:407-11. doi: 10.4103/aca.ACA_94_19. PubMed Link