Data collection and interpretation plays a major role in strength and conditioning practice. The most common situation to which this applies is the measurement of physical capabilities, and the subsequent analysis of testing scores. However, the importance of data handling skills and statistical analysis is not always adequately emphasised during applied strength and conditioning education, which may result in some individuals lacking confidence in this area. In particular, it is important that the S&C practitioner understands the difference between an observed score and the true score, and how error in measurement reduces our ability to detect real change in testing scores. The following article aims to provide an applied step-by-step guide to calculating typical error, determining reliability, and establishing the minimum difference to be considered real.