TABLE 1

Basic statistical methods used in medical research by research goal and type of outcome variable

Research goal	Type of outcome variable
Research goal	Measurement from symmetric distribution	Measurement from very skewed distribution	Categorical variable	Time to event
Describing one variable	Mean±sd	Median, interquartile range	Proportion	Kaplan–Meier curve
Comparing two independent groups	Comparing means with independent samples t-test	Comparing medians with Mann–Whitney test	Cross-tabulation with Chi-squared test	Kaplan–Meier curves and log-rank test
Comparing three or more independent groups	Comparing means with one-way ANOVA	Comparing medians with Kruskal–Wallis test	Cross-tabulation with Chi-squared test	Kaplan–Meier curves and log-rank test
Comparing two repeated measurements	t-test for repeated measurements	Wilcoxon test	McNemar's test
Comparing three or more repeated measurements	Repeated-measures ANOVA	Friedman test
Quantifying association between two variables	Pearson correlation	Spearman correlation	Cross-tabulation with Chi-squared test, risk ratio or odds ratio statistics
Explaining variation with several explanatory variables	Multivariable linear regression	Negative binomial regression	Logistic regression	Cox proportional hazard regression

Reproduced and modified from [10].