In health research, trial results are often presented as risk ratios such as Odds Ratio (OR), Relative Risk (RR), or Number Needed to Treat (NNT). In healthcare, "risk refers to the probability of a bad outcome in people with the disease" (Reference: Irwig L, Irwig J, Trevena L, et al. Smart Health Choices: Making Sense of Health Advice. London: Hammersmith Press; 2008. Chapter 18, Relative risk, relative and absolute risk reduction, number needed to treat and confidence intervals. Available from: https://www.ncbi.nlm.nih.gov/books/NBK63647/) .
The resources in the section will help you understand the differences between these formats, and when to use each one.
Statistics and Data Interpretation for Social Work by 
Statistics for Nursing: a Practical Approach by
1. The formula for various risk formats are part of the BMJ "Learn EBM" series under "How to Calculate Risk" https://bestpractice.bmj.com/info/toolkit/learn-ebm/how-to-calculate-risk/
2. How to make sense of risk written for a patient/ layperson: Irwig L, Irwig J, Trevena L, et al. Smart Health Choices: Making Sense of Health Advice. London: Hammersmith Press; 2008. Chapter 18, Relative risk, relative and absolute risk reduction, number needed to treat and confidence intervals. Available from: https://www.ncbi.nlm.nih.gov/books/NBK63647/
