Keep an eye out for a blog post discussing how the level of sample homogeneity — and other factors — might affect thematic saturation, and therefore sample size! Very interesting. Very useful. If I understood the conclusions correctly, it does go back to traditional rule of thumb approaches; i. The catch, or course, is that one should be carefully reviewing scripts as data is collected. I like the idea that it confirms one may make advance decisions on set targets.
Thanks, Jane! Wonderful overview of the literature, thank you so much for this! However, I always take these numbers with a pinch of salt, saturation will obviously vary greatly with topic area and research question. Yes, absolutely, Daniel! Thanks for your comment and link. Stay tuned for the next post in this series that will address some of the factors that affect saturation — to help identify whether a small or large pinch of salt should go into saturation-based qualitative sample size calculations!
Thanks for this post — really useful. One question I have is, did any of these studies consider the interviewing skills of the interviewer? Or mention what training the interviewers had in advance of doing the semi-structured interviews?
Hi Mia, great questions! As an aside from the sampling discussion, interviewer training really is key to generating good qualitative data — and not just training in terms of interviewing skill, but also in making sure that everyone has a common understanding of the research objectives.
Some people have a more natural affinity for interviewing than others, but if you can provide your interviewers with pretty immediate feedback e. May I ask if you were conducting surveys via email — what would be an acceptable number of completed surveys to aim for? Thanks for this illuminating post. I have now collected data from 2 different states were I conducted 13 interviews and 3 FGDs in the first and 8 interviews and 1 FGD in the next. When I started collecting data from the second state, I reached data saturation much quicker and for the FGDs i was not getting much different data from the first state.
I am now wondering if I have taken the right approach. Was the interviews and FGDs recommended per each round of data collection? Hi Abisola, Yes, it sounds like you interpreted the recommendations correctly — that those sample sizes are per sub-population of interest. In your case, I would have considered the two states as two sub-populations, as you did. Emily and Greg, this is brilliant!
Just what I needed today, and described in such simplistic and fun way. Your email address will not be published. Notify me of follow-up comments by email. Notify me of new posts by email. This site uses Akismet to reduce spam. Learn how your comment data is processed.
This blog post is the final in a series of three sampling-focused posts. Sampling to reach saturation? Looking up Morgan [ 1 ], we found that he claims that most studies use four to six groups because they then reach saturation, but he also underlines that the more categories of participants and less standardisation of questions, the higher number of focus groups. Three of the 37 studies reported practical reasons for the number of focus groups conducted.
The information offered regarding recruitment constraints was incomplete as, for example, in this explanation:. The number of available participants was limited and the number of focus groups was therefore few [ 56 ].
Two of the explanations appeared to be tied to difficulties in recruiting participants to additional groups [ 56 , 57 ], while one mentioned limited resources "budgetary and staffing constraints" which led the researchers to decide pre-study to conduct five focus groups [ 38 ].
This last study also claimed to have reached saturation without stating this as the procedure for deciding number of groups :. However, data analysis indicates that all themes reached saturation, meaning additional participants would likely not have added to the depth or breadth of parent responses [ 38 ].
An additional eight studies also described recruitment limitations, but only as an explanation for the total number of participants, not for how many groups the participants were divided into. In these studies, the size of the groups seems to have been decided beforehand, due to text book recommendations, and thus the number of groups was given by the total number of already recruited participants divided by the number of participants per group. The results from our searches from , and support the claims that there has been an increase in focus group studies over the last ten years.
The wide range of health journals publishing focus group studies in indicates that this method is now widely accepted. At the same time, the fact that many journals publish only one or two focus group studies a year could also mean that the methodological competence among editors and reviewers to assess focus group studies is lacking. The great variation in the number of focus groups that we registered was surprising, and was wider than authors of teaching materials and text books assume.
For example Stewart et al [ 13 ] claim: "Most focus group applications involve more than one group, but seldom more than three or four groups. Overall, reporting of sample size and explanations for this size was poor. Where such explanations were given, our study confirms the dominant role of the concept of data saturation. We also discovered that all explanations were found in studies of between two and 13 groups. Some of these studies refer to existing pragmatic guidelines to justify their numbers, although the two to five focus groups per category recommended in these guidelines sometimes appear to have become two to five groups in total in the studies.
We could speculate that studies using only one focus group, a number that goes against the rules of thumb offered by these guidelines, is simply too hard to justify and explanations are therefore evaded. Also, all the single group studies were mixed methods studies, where the focus group typically was used as a pilot to develop or test a questionnaire for the survey part of the study.
In these examples, it is understandable that the focus group is offered less attention than the main part of the study. At the other end of the scale, one could also speculate that when the sample size reaches two-digit numbers, a "quantitative study logic" kicks in where a big N is seen as a positive asset and therefore less important to justify.
Roughly half of the studies that referred to data saturation as an explanation for number of focus groups did not appear to be consistent in their use of approach. These findings support earlier reviews of the field. Twohig and Putnam [ 7 ], were also startled by the variation in procedures and reporting of focus group studies, and Webb and Kevern [ 58 ], who reviewed focus group studies in nursing research, found that authors used terms such as "Grounded theory" in non-rigorous ways.
These authors also conclude that researchers, on the whole, did not follow basic premises for reaching saturation such as concurrent data generation and analysis, or an "iterative process" [ 15 ].
Our study shows the same tendencies, and suggests that the increased use of focus groups in health care studies has not led to an improvement in the quality of reporting. We were also struck by what we did not find. In our own experience with focus group research, recruitment problems are much more common than this review indicates. In addition, a number of practical limitations arise that can limit the number of focus groups conducted, including limited money and time.
Excepting one study, where resource constraints were brought up, the only practical limitations mentioned were difficulties in recruiting more participants. Another non-finding was that none of the studies discussed a large number of focus groups as a potential limitation of the study.
Given frequent references in these studies to the advantages of qualitative methodology for eliciting richness and depth of the data, it is not evident why the authors never used the argument that data from a large number of focus groups is difficult to analyse thoroughly.
The inadequate reporting indicated in our study could reflect the fact that most health science journals do not require specific standards of reporting from contributors presenting qualitative research. However, the poor reporting among these authors also seem to indicate confusion about when and how to decide the number of focus groups, which may reflect a lack of properly described, consistent advice to researchers wishing to carry out focus group-based data collection.
The lack of attention to sample size in the teaching material could easily be perceived as an indication that sample size is unimportant in such studies.
In addition, the advice that is offered is confusing and sometimes conflicting. While the Glaser and Strauss's procedure of theoretical saturation instructs authors to use theoretical sampling and to analyse and collect data iteratively until saturation is achieved, it does not offer a detailed interpretation of how to operationalise this approach.
The "how to do" literature on focus group methodology, on the other hand, offers pragmatic advice regarding the number of groups that researchers should expect to conduct before point of saturation is reached, but do not clarify how to decide about point of saturation in practice. This advice may thus tempt researchers to follow their suggestions for number of groups and do the analysis after collecting all data.
Then, as they expect data to be saturated, their critical sense could be undermined when drawing conclusions about saturation. Despite problems associated with the practical application of the concept of data saturation, it seems to have become something of an ideal in qualitative health research.
This could be due to the fact that it is the only theory that offers advice, albeit, poorly operationalised, about the exact number of interviews needed. It is plausible that editors in the traditionally positivistic realm of health research are inclined to prefer explanations for exact number of groups. Practical limitations might not be as acceptable, especially not explicit references to economic or resource limitations.
In the methodology discussions of these studies, authors often point out that small sample sizes are legitimate in qualitative studies. At the same time, they often feel the need to justify small sample sizes which they invariably see as a study limitation. This may be a consequence of the fact that qualitative studies are still in a minority in health science journals.
Here, more positivistic traditions may make it difficult to argue that a qualitative study can have too many groups. Nevertheless, the quality of qualitative studies does depend on the depth and richness of the data and its analysis. Reference to the trade-off between number of focus groups and the thickness of our description should therefore be an acceptable explanation for a limited sample size.
There is also an ethical side to sample size: an excessive number of interviews means placing a burden on patients or health workers that is not legitimised by added scientific value and can thereby be seen as unethical.
A limitation of our study was that our sample was taken from open-access journals. Current research does suggest that articles published in open-access journals are more often cited than other articles [ 59 ]. It is therefore possible that the articles we evaluated are of a higher profile than other non-open-access articles and may be more likely to serve as examples for other researchers. While we emphasise that our findings are primarily valid for open access studies, it therefore seems all the more important to secure the quality of these reports.
We decided to include all studies claiming to be focus group studies. We have therefore also included mixed method studies, where the focus group interviews are often part of a predominantly quantitative design. In such studies the authors may not aim to adhere to standards for reporting qualitative studies.
On the other hand, it could be argued that researchers who report that they have used focus groups should adhere to the methodological standards for such studies. There are some uncertainties in our findings due to the poor reporting in the material.
For instance, it was sometimes difficult to decide whether an explanation for number of focus groups had been given and what this explanation was. The number of studies that give practical reasons for their number of groups or that refers to data saturation is therefore slightly uncertain. Because of meagre and unclear reporting, it was also difficult to tell whether the studies that claimed to have decided on sample size through an iterative research process and point of saturation did, in fact, analyse their data after data collection had ended.
Usually, several confusing aspects of the reporting appeared in the same studies. As our study looked at focus groups only, future research should consider whether sample size reporting of individual interviews shows similar problems. While researchers should always provide correct and detailed information about the methods used, our study shows poor and inconsistent reporting of focus group sample size. Our study also indicates that poor reporting could reflect a lack of clear, evidence-based guidance about how to achieve optimal sample size.
To amend this situation, text books and teaching material based on empirical studies into the use of focus group methodology and applicable and precise recommendations are needed. Ironically, one barrier to high-quality methodological studies is the current lack of proper reporting by authors of primary studies.
Both authors have conducted multimethod research, including focus group studies, partly on assignment and have mainly published in health science journals. Morgan DL: Focus Groups. Annual Review of Sociology. Article Google Scholar. Google Scholar. Int J Qual Health Care. Book Google Scholar.
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Ann Fam Med. Curr Med Res Opin. Health Promot Pract. Br J Gen Pract. Triads also allow moderators to observe how triangulation may influence perceptions and responses. When it comes to focus groups, more is not always better. Focus groups are at their most effective when they have between six to seven participants. March 3, There are a number of methodologies that market researchers rely on when conducting qualitative research. Tweet Share Share Email.
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