What Influences Saturation? Estimating Sample Sizes in Focus Group Research

Abstract

Saturation is commonly used to determine sample sizes in qualitative research, yet there is little guidance on what influences saturation. We aimed to assess saturation and identify parameters to estimate sample sizes for focus group studies in advance of data collection. We used two approaches to assess saturation in data from 10 focus group discussions. Four focus groups were sufficient to identify a range of new issues (code saturation), but more groups were needed to fully understand these issues (meaning saturation). Group stratification influenced meaning saturation, whereby one focus group per stratum was needed to identify issues; two groups per stratum provided a more comprehensive understanding of issues, but more groups per stratum provided little additional benefit. We identify six parameters influencing saturation in focus group data: study purpose, type of codes, group stratification, number of groups per stratum, and type and degree of saturation.

Keywords: USA; diabetes; focus group discussions; methodology; qualitative; qualitative research; sample size; saturation.

Conflict of interest statement

The authors declare that there is no conflict of interest.

Figures

Figure 1.

Timing of code development and code saturation. Note.Two deductive codes were developed in Focus Group 2. These codes were derived from questions in the discussion guide that were not probed in Focus Group 1 but were probed in Focus Group 2. FGD = focus group discussion; Y = Younger; M = Male; O = Older; F = Female.

Figure 2.

Timing of code development—Actual versus randomized order of FGDs. Note.FGD = focus group discussion.

Figure 3.

Timing of code development by code prevalence and type. Note. FGD = focus group discussion. aDashedline indicates average code prevalence across all data at 7.2 FGDs.

Figure 4.

Timing of first use of codes and their meaning saturation. * concrete code.