Saturation controversy in qualitative research: Complexities and underlying assumptions. A literature review

Figures & data

Table 1. Different Forms of Saturation and their Explanations

Type	Explanation	Focal point	References
Theoretical saturation	Describes the generation of theoretical or conceptual categories as guided by the grounded theory. Relates to when are the concepts or dimensions of a theory are fully reflected in the data.	Sampling Analysis	(Glaser & Strauss, 1967; Morse et al., 2014) Starks and Trinidad (2007, p. 1375) as cited in Saunders et al. (2018), (Morse, 2015).
Thematic saturation	Inductive-Linked the point where no new codes and/or themes are emerging from the data. A priori- hinges on the extent to which the determined codes or themes epitomise or illustrate the data.	Analysis Sampling	(Hancock et al., 2016; Hennink et al., 2017; Urquhart, 2012)
Data Saturation	Explicates the level to which new data repeats what was expressed in previous data (data replication).	Data collection and analysis	(Fusch & Ness, 2015)
Meaning Saturation	Relates to the quality of data, “richness and thickness” when no additional information from the data emerges. Quality, deep, detailed and relevant data has been gathered.	Throughout the research process (planning, data collection and analysis	(Hennink et al., 2017; Hennink et al., 2019)

Adapted from Saunders et al. (2018) and enhanced from various researchers.

Table 2. Qualitative Design, their Purposes and Ideal Data Collection Instruments

Qualitative Research Design	Purpose of Design	Data Collection methods
Ethnography	Cultural interpret data. Important features are naturalism, small samples, multiple data sources, ‘emic’ and ‘etic’ (Lambert et al., 2011)	Participant observation mostly used, In-depth interviews and focus groups suitable for use
Phenomenology	Aims to understand phenomenon in-depth through studying human experience. Meaning is derived from the feelings, perceptions and cognitions (McKerchar, 2008; Wilson, 2015)	In-depth inter views suitable for use
Grounded	Seeks to build theory from a research situation. It is iterative and integrative research design (McGhee et al., 2007)	Participant observation rarely used, in-depth and focus groups interviews suitable for use
Content Analysis	Systematically analyse textual data, making replicable and valid inferences with the hope of generating knew knowledge, insights as well as condense the data (Elo & Kyngäs, 2008)	Participant observation used sometimes, in-depth inter views and focus groups suitable for use

Adapted from Moser and Korstjens (2018).

Table 3. Type of Sampling in Qualitative research and their Descriptions

Type of Sampling	Description
Purposive Sampling	Selection of participants based on the researcher’s personal judgement, based on the informative nature or “information power” of participants. For example experience, institutional memory, specificity, purpose of the study and their relevance to the study.
Criterion	Choosing participants on the basis of a pre-determined criteria of importance.
Theoretical	Choice of participants is driven by emerging findings to ensure sufficiency in addressing theoretical concepts that are key to the research.
Convenience	Sampling is based on availability, the readily and easily available.
Snowballing	Selection is informed by referrals by participants previously selected. For example, one tax consultants refers you to two other more knowledgeable and experienced tax consultants that he knows from their association in the tax field.
Maximum Variation	Choice of participants based on a broad range of variations in the backgrounds of these participants.
Extreme Case	Purposeful choosing of the most unusual cases.
Typical Case	Most typical and average participants are chosen.
Confirming and Disconfirming	Sampling that is meant to support checking or challenging of emerging trends or patterns in the data

Source: Adapted from Moser and Korstjens (2018).

Table 4. Studies on Saturation in Qualitative research, suggested sample sizes and rationale

Sample size	Rationale	Researcher
12 semi-structured interviews	Convenient sampling, initial sample based on suggestions by Mason (2010)	(Constantinou et al., 2017)
6 to 12 interviews	More comprehensive data can be collected from in-depth. Small samples more appropriate in homogeneous sample and experts in the field	(Guest et al., 2006; Kuzel, 1992)
5 interviews for code saturation and more interviews in order to achieve saturation on meanings	Code saturation Meaning Saturation	(Hennink et al., 2017)
25 to 200 interviews	Open ended surveys	(Tran et al., 2017)
6 interviews	Large samples could compromise credibility and contextualisation of data and quotations	(Morse, 2000)

Source: Author’s compilation from various sources.

Table 5. Studies on Focus groups, suggested numbers and Justification

Number of focus groups	Justification	Researcher (s)
6 focus groups adequate to attain code saturation but more needed to achieve meaning saturation (achieved at 9^th focus group and conceptual notions saturated at 24^th interview).	Code saturation can be easily attained (By 6^th interview 94% of all codes had been attained and 96% of high prevalent codes had been identified), yet meaning saturation entails comprehending issues fully which is not easy	(Hennink et al., 2019)
6 Focus groups	64% of codes generated at 1^st interview, 84% of the code at 3^rd interview and 80 to 90% of the thematic codes emerged at 6^th focus group	(Guest et al., 2017)
5 Focus groups	Used maximum variation sampling to create a diverse sample. Employed inductive approach to generate themes and deductive approach in applying the themes	(Coenen et al., 2012; Hancock et al., 2016)

Source: Various Studies.

Glaser, B., & Strauss, A. (1967). Thediscovery of grounded theory. Strategies for qualitative research. The Sociology Press.

 Google Scholar

Morse, W. C., Lowery, D. R., & Steury, T. (2014). Exploring saturation of themes and spatial locations in qualitative public participation geographic information systems research. Society & Natural Resources, 27(5), 557–571. https://doi.org/10.1080/08941920.2014.888791

 Web of Science ®Google Scholar

Saunders, B., Sim, J., Kingstone, T., Baker, S., Waterfield, J., Bartlam, B., Burroughs, H., & Jinks, C. (2018). Saturation in qualitative research: Exploring its conceptualization and operationalization. Quality & Quantity, 52(4), 1893–1907. https://doi.org/10.1007/s11135-017-0574-8

 PubMed Web of Science ®Google Scholar

Morse, J. M. (2015). Data were saturated. Sage Publications Sage CA.

 Google Scholar

Hancock, M. E., Amankwaa, L., Revell, M. A., & Mueller, D. (2016). Focus group data saturation: A new approach to data analysis. The Qualitative Report, 21(11), 2124.

 Web of Science ®Google Scholar

Hennink, M. M., Kaiser, B. N., & Marconi, V. C. (2017). Code saturation versus meaning saturation: How many interviews are enough? Qualitative Health Research, 27(4), 591–608. https://doi.org/10.1177/1049732316665344

 PubMed Web of Science ®Google Scholar

Urquhart, C. (2012). Grounded theory for qualitative research: A practical guide. Sage.

 Google Scholar

Fusch, P. I., & Ness, L. R. (2015). Are we there yet? Data saturation in qualitative research. The Qualitative Report, 20(9), 1408.

 Web of Science ®Google Scholar

Hennink, M. M., Kaiser, B. N., & Weber, M. B. (2019). What influences saturation? Estimating sample sizes in focus group research. Qualitative Health Research, 29(10), 1483–1496. https://doi.org/10.1177/1049732318821692

 PubMed Web of Science ®Google Scholar

Lambert, V., Glacken, M., & McCarron, M. (2011). Employing an ethnographic approach: Key characteristics. Nurse Researcher, 19(1), 17–24. https://doi.org/10.7748/nr2011.10.19.1.17.c8767

 PubMedGoogle Scholar

McKerchar, M. A. (2008). Philosophical paradigms, inquiry strategies and knowledge claims: Applying the principles of research design and conduct to taxation.

 Google Scholar

Wilson, A. (2015). A guide to phenomenological research. Nursing Standard (2014+), 29(34), 38. https://doi.org/10.7748/ns.29.34.38.e8821

 PubMedGoogle Scholar

McGhee, G., Marland, G. R., & Atkinson, J. (2007). Grounded theory research: Literature reviewing and reflexivity. Journal of Advanced Nursing, 60(3), 334–342. https://doi.org/10.1111/j.1365-2648.2007.04436.x

 PubMed Web of Science ®Google Scholar

Elo, S., & Kyngäs, H. (2008). The qualitative content analysis process. Journal of Advanced Nursing, 62(1), 107–115. https://doi.org/10.1111/j.1365-2648.2007.04569.x

 PubMed Web of Science ®Google Scholar

Moser, A., & Korstjens, I. (2018). Series: Practical guidance to qualitative research. Part 3: Sampling, data collection and analysis. European Journal of General Practice, 24(1), 9–18. https://doi.org/10.1080/13814788.2017.1375091

 PubMed Web of Science ®Google Scholar

Mason, M. (2010). Sample size and saturation in PhD studies using qualitative interviews [Paper presentation]. Forum qualitative Sozialforschung/Forum: qualitative social research.

 Google Scholar

Constantinou, C. S., Georgiou, M., & Perdikogianni, M. (2017). A comparative method for themes saturation (CoMeTS) in qualitative interviews. Qualitative Research, 17(5), 571–588. https://doi.org/10.1177/1468794116686650

 Web of Science ®Google Scholar

Guest, G., Bunce, A., & Johnson, L. (2006). How many interviews are enough? An experiment with data saturation and variability. Field Methods, 18(1), 59–82. https://doi.org/10.1177/1525822X05279903

 Web of Science ®Google Scholar

Kuzel, A. (1992). Sampling in qualitative inquiry. In B. Crabtree & W. Miller (Eds.), Doing qualitative research (pp. 31–44). Sage.

 Google Scholar

Tran, V.-T., Porcher, R., Tran, V.-C., & Ravaud, P. (2017). Predicting data saturation in qualitative surveys with mathematical models from ecological research. Journal of Clinical Epidemiology, 82(71–78), e72. https://doi.org/10.1016/j.jclinepi.2016.10.001

 Google Scholar

Morse, J. M. (2000). Determining sample size. Sage Publications Sage CA.

 Google Scholar

Guest, G., Namey, E., & McKenna, K. (2017). How many focus groups are enough? Building an evidence base for nonprobability sample sizes. Field Methods, 29(1), 3–22. https://doi.org/10.1177/1525822X16639015

 Web of Science ®Google Scholar

Coenen, M., Stamm, T. A., Stucki, G., & Cieza, A. (2012). Individual interviews and focus groups in patients with rheumatoid arthritis: A comparison of two qualitative methods. Quality of Life Research, 21(2), 359–370. https://doi.org/10.1007/s11136-011-9943-2

 PubMed Web of Science ®Google Scholar