Should a Thesis Predetermine a Qualitative Sample-Size Range?

Should You Specify an Exact Number of Qualitative Participants Before Your Thesis Begins?

You are preparing a qualitative thesis proposal and your adviser asks how many participants you intend to interview. You propose fifteen to twenty participants, explaining that the final number will depend on the adequacy of the information collected.

Your adviser wants an exact number. Your ethics application also requires an anticipated recruitment total. Yet the methodology you selected allows data collection and analysis to inform one another, meaning that you cannot know in advance precisely how much information participants will provide.

Should you commit to twenty interviews, establish a provisional range, or avoid specifying a number altogether?

The difficulty is not simply administrative. A thesis must demonstrate that recruitment is feasible and ethically justified while preserving the sampling logic required by its methodology.

A Predetermined Range Is Often Appropriate, but It Should Be Justified and Methodologically Flexible

Planning a Qualitative Thesis Sample Without Creating an Arbitrary Quota

Why Do Thesis Proposals Require Participant Numbers?

A thesis proposal must establish that the planned research can be conducted responsibly and within available resources.

Participant estimates help supervisors and research committees evaluate recruitment feasibility, expected workload, data-management requirements, and the likely duration of fieldwork.

Ethics committees may also need to understand the anticipated number of people exposed to recruitment procedures, interviews, or other research activities.

These are legitimate planning considerations. They do not necessarily imply that qualitative sample adequacy can be determined with numerical certainty before data collection.

Institutional requirements vary. Some protocols request an exact anticipated number, while others permit a range or a maximum recruitment ceiling. Researchers should follow the applicable approved protocol and amendment procedures.

What Is the Difference Between a Target, Range, Minimum, and Maximum?

These terms serve different purposes and should not be used interchangeably.

A proposal stating that fifteen to twenty participants are anticipated should explain what the range represents. It should not imply that reaching fifteen automatically demonstrates adequacy or that twenty participants necessarily exhaust the relevant information.

Why Can an Exact Number Be Difficult to Justify Prospectively?

Qualitative interviews do not always contribute equivalent amounts of information.

Participants may differ in the relevance of their experiences, willingness to discuss sensitive matters, and ability to provide detailed accounts. Early analysis may also reveal perspectives that the original recruitment plan did not adequately anticipate.

For methodologies involving iterative sampling, such developments may justify recruiting additional participants or seeking different participant characteristics.

Consequently, an exact prospective number may create a misleading impression that the informational requirements are already known.

Nevertheless, some qualitative designs use relatively fixed samples for legitimate reasons, including bounded case studies and intensive idiographic analyses. Flexibility is not an obligation independent of methodology.

How Should the Research Aim Inform the Initial Range?

The research aim determines what kinds of experiences and perspectives must be examined.

A focused study of how experienced online instructors develop a particular assessment type may require less breadth than a comparative study involving teachers from several disciplines and institutions.

However, a narrowly focused aim can still require extensive analysis when experiences are complex or highly varied.

Before selecting a range, researchers should identify the phenomenon, relevant participants, essential variation, and intended analytical contribution.

The relationship between the research aim and qualitative sample size provides a more defensible starting point than copying a conventional interview count.

Can Information Power Justify a Provisional Range?

Yes. Malterud, Siersma, and Guassora (2016) proposed information power as a framework for reasoning about sample adequacy in qualitative interview studies.

Its five dimensions concern study aim, sample specificity, established theory, dialogue quality, and analysis strategy.

Researchers can evaluate several of these considerations prospectively. For example, they may know that the study has a focused aim and that participants will be selected for direct experience of the phenomenon.

Other dimensions, particularly actual dialogue quality, become clearer during data collection.

The information power framework can therefore support an initial range and its subsequent review. It does not provide a formula that converts the five dimensions into an exact number of interviews.

Can Saturation Be Used to Establish a Range Before Interviews?

Previous empirical studies of saturation may inform prospective recruitment planning, but saturation itself is ordinarily assessed through accumulating data and analysis.

Guest, Bunce, and Johnson (2006) examined thematic saturation in a particular interview dataset. Hennink and Kaiser (2022) synthesized empirical studies reporting saturation under different research conditions.

These findings are useful for understanding possible recruitment requirements, but they do not establish a universally sufficient number.

Researchers should also distinguish code saturation from meaning saturation, since identifying recurring codes may require less data than developing a nuanced interpretation of those codes.

Most importantly, saturation is not appropriate for every qualitative methodology. It should not be inserted into a proposal merely to justify a numerical range.

Does the Appropriate Planning Strategy Differ Across Methodologies?

Yes. A prospective recruitment plan should reflect how the chosen methodology develops and evaluates evidence.

These approaches are illustrative. The methodological tradition and actual analytical procedure should govern the justification.

Should the Lower Bound Be Treated as a Mandatory Minimum?

Not necessarily. A lower bound may be useful for scheduling and resource planning, but its methodological significance must be explained.

For example, a researcher might anticipate that fewer than twelve interviews would provide limited coverage of the relevant participant variation. That expectation should be supported by the study's sampling rationale rather than presented as a universal rule.

If analysis indicates that the material is already adequate before the lower bound is reached, the researcher must consider the methodology, approved protocol, and strength of that assessment.

Conversely, reaching the lower bound does not justify stopping when essential perspectives or analytical questions remain unaddressed.

Should the Upper Bound Be a Hard Stopping Rule?

An upper bound may be necessary for ethics approval, resource allocation, or practical feasibility.

However, reaching it does not establish that analytical adequacy has been achieved.

If the approved maximum is reached while important information remains missing, the researcher may need to seek an amendment, revise the research scope, or acknowledge the resulting limitations.

Continuing recruitment beyond an approved limit without the required authorization would be inappropriate.

The distinction between an administrative ceiling and an analytical stopping criterion should be explicit.

Can the Final Sample Fall Outside the Proposed Range?

It can, depending on the approved research protocol and the reasons for the change.

A study may require additional participants because analysis identifies missing experiences or insufficient conceptual development.

Alternatively, recruitment may end below the planned range because the eligible population is smaller than anticipated or participants decline to participate.

These circumstances should not be described as equivalent. An analytically justified change differs from recruitment ending because of practical constraints.

Material departures from the approved protocol may require ethics or institutional authorization before implementation.

What If a Thesis Adviser Requires Exactly Fifteen Participants?

Researchers should clarify whether the requirement is administrative, methodological, or based on an institutional template.

If the methodology supports a fixed sample, the proposed number can be justified through the research aim and intended analysis.

If the methodology requires iterative recruitment, the proposal can distinguish the initial target of fifteen from the criteria used to evaluate adequacy.

A constructive explanation should address how the study will remain feasible and ethically manageable while preserving methodological coherence.

There is no need to frame flexibility and advance planning as mutually exclusive.

How Should Recruitment Be Monitored?

Researchers should maintain a recruitment record showing how many individuals were approached, screened, eligible, consented, and interviewed.

Where the methodology permits concurrent analysis, analytical memos can document whether interviews are providing relevant information and whether additional perspectives are needed.

The recruitment record and analytical record serve different purposes. One describes participation, while the other helps justify information adequacy.

For studies using an appropriate saturation procedure, the researcher may document the contribution of successive interview batches. Other approaches may evaluate depth, conceptual development, or case completeness.

What Happens When the Thesis Timeline Is Too Short?

Qualitative research requires time not only for recruitment and interviewing but also for transcription, familiarization, analysis, interpretation, and writing.

A large planned sample may become counterproductive when the researcher cannot analyze the resulting material with sufficient depth.

However, limited time does not automatically justify a smaller sample as methodologically adequate.

If the proposed study is infeasible, researchers should reconsider its scope, recruitment strategy, or timeline before data collection where possible.

The potential effect of excessive recruitment on analytical depth is particularly relevant to intensive interpretive studies.

How Should the Planned Range Be Written in a Thesis Proposal?

A defensible statement should identify the initial target, sampling strategy, eligibility criteria, and rationale for the proposed range.

It should then explain how adequacy will be assessed and whether the design permits recruitment adjustments.

For example, a researcher might state that approximately fifteen to twenty teachers will be recruited purposively because they have direct experience developing online assessments, with the final sample reviewed against the informational and analytical requirements of the study.

The numbers should be presented as study-specific planning assumptions rather than universally established qualitative thresholds.

How Should the Final Sample Be Justified in the Completed Thesis?

The completed thesis should report both the planned and achieved sample sizes, particularly when they differ.

The researcher should describe the recruitment process, relevant participant characteristics, changes to the sampling strategy, and the basis for judging the achieved data sufficient.

If the final sample was limited by time, access, or nonparticipation, those constraints should be acknowledged rather than retrospectively relabeled as saturation or information power.

Vasileiou and colleagues (2018) found substantial variation in how published qualitative interview studies justified sample-size sufficiency, underscoring the value of explicit methodological reporting.

The final participant count is part of the evidence supporting the study, not a substitute for explaining its adequacy.

Planning a Thesis Interview Range Without Making It an Arbitrary Quota

The example illustrates how a provisional range can support practical planning while remaining responsive to analytical needs.

It also demonstrates why the final number must be justified independently of the fact that it falls within the originally proposed range.

Common Misconceptions About Predetermined Qualitative Samples

Specify a Defensible Recruitment Plan and Explain Its Flexibility

Begin with the methodology and research aim, then develop a realistic target or range based on participant relevance, intended variation, and analytical requirements.

Explain what would justify continuing, modifying, or stopping recruitment, subject to the approved protocol.

A thesis proposal should demonstrate that the researcher has a credible plan, not pretend that every recruitment outcome can be known in advance.

The final thesis should explain what actually occurred and why the achieved sample supports the analysis.

Before Finalizing a Qualitative Thesis Sample-Size Range

Frequently Asked Questions About Qualitative Thesis Sample-Size Planning

Predetermine the Recruitment Plan, Not an Unsupported Claim of Adequacy

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