One of the key goals of assessment in medical education is the minimisation of all errors influencing a test in order to produce an observed score which approaches a learner's 'true' score, as reliably and validly as possible. In order to achieve this, assessors need to be aware of the potential biases that can influence all components of the assessment cycle from question creation to the interpretation of exam scores. This Guide describes and explains the processes whereby objective examination results can be analysed to improve the validity and reliability of assessments in medical education. We cover the interpretation of measures of central tendency, measures of variability and standard scores. We describe how to calculate the item-difficulty index and item-discrimination index in examination tests using different statistical procedures. This is followed by an overview of reliability estimates. The post-examination analytical methods described in this guide enable medical educators to construct reliable and valid achievement tests. They also enable medical educators to develop question banks using the collection of appropriate questions from existing examination tests in order to use computerised adaptive testing.