APA Dictionary of Psychology

a scheme or list of mutually exclusive labels, categories, and so forth—each of which characterizes a coherent dimension of interest—used for classifying information obtained by observing others. It is an essential component of any observational study as it clarifies what data should be collected and how, providing definitions of each code along with examples. For instance, a researcher investigating infant behavior might develop the following observation coding system: (1) quietly alert, (2) crying, (3) fussing, and (4) sleeping. Thus, for every time during a specific observation period that an observer sees the baby acting alert, they would record a 1 on their data form; for every time the observer sees the baby crying, they would record a 2, and so forth.