Summary statistics for dichotomous outcome data 11

This module introduces some basic statistics for dealing with dichotomous outcomes. We discuss ways of summarising results and determining treatment effects within single trials, and prepare for meta-analysis.

Learning objectives

  • Understand the difference between risk and odds
  • Be able to calculate risk ratios and odds ratios from a 2×2 table for a single trial
  • Be able to calculate risk differences and numbers needed to treat (NNT) from a 2×2 table for a single trial
  • Be able to report and interpret risk ratios, odds ratios, risk differences and NNTs and their confidence intervals
  • Be able to choose a suitable summary statistic for the meta-analysis and reporting of dichotomous data

Relevant sections of the Reviewers’ Handbook

  • Section 8 – ‘Effect measures for single studies’

Where does this go in a Cochrane review?

The information in this module will be relevant to many parts of your review

  • In the data analysis part of the Methods section of a protocol or review, where you will describe what statistical techniques you are planning to use
  • When (or if) you actually perform meta-analyses using the analysis part of RevMan or other software
  • In the presentation of results in the Results section of the review
  • In the interpretation of results, in the Discussion of your review