Table 1 The relationship between data adequacy and data saturation

A related concept to data adequacy is the concept of data saturation. In primary research, “data saturation” is often used to refer to the point in data collection and analysis when “no new themes, findings, concepts or problems were evident in the data” [29]. When used in this way, the concept of data saturation is clearly different from the concept of data adequacy as the former focuses on identifying new themes while the latter concept focuses on the extent to which an individual theme or finding is adequately supported by the data. Within grounded theory, the concept of data saturation is more ambitious, however, and “relates not merely to “no new ideas coming out of the data” but to the notion of a conceptually dense theoretical account of a field of interest in which all categories are fully accounted for, the variations within them explained, and all relationships between the categories established, tested and validated for a range of settings” [25]. This second use of the concept is closer to the concept of data adequacy as both focus on the extent to which the data has allowed us to explore the topic in sufficient depth. But there are also differences between these concepts. Researchers applying the concept of data saturation in the context of primary research use this concept as an ideal or goal when collecting and analysing data, and strive to collect new data until saturation has been met. When applying the concept of data adequacy in the context of a qualitative evidence synthesis, on the other hand, researchers assess data that has already been collected, and focus on identifying concerns with this data. As the process of data saturation is potentially limitless; and determining the point at which “saturation” has happened is difficult, if not impossible [26]; the concept of data adequacy may be a more pragmatic and feasible approach.