How to Determine Sample Size for a Qualitative Education Doctoral Dissertation

How to Determine Sample Size for a Qualitative Education Doctoral Dissertation

Determining the sample size for a qualitative education doctoral dissertation is not based on statistical formulas or power calculations. Instead, it is guided by the depth of information needed, the research design, and the point at which no new educational insights emerge from the data.

In qualitative education research, the goal is not to generalize findings to a population, but to develop a deep understanding of educational experiences, perceptions, and processes.

In simple terms, qualitative sample size answers: “How many participants are needed to fully understand the educational phenomenon being studied?”

What Is Sample Size in Qualitative Education Research?

The sample size refers to the number of participants included in a qualitative study, such as:

• Teachers

• Students

• School administrators

• Parents

• Education specialists

Unlike quantitative research, qualitative education studies focus on:

• Depth of experience

• Meaning and interpretation

• Contextual understanding

• Rich descriptive data

Key Principle: Data Saturation

The most widely used concept for determining qualitative sample size is data saturation.

Data saturation means:

The point at which additional data collection no longer produces new themes, ideas, or insights.

In education research, this occurs when:

• Teacher responses become repetitive

• Student experiences show similar patterns

• No new instructional or learning themes emerge

Example:

If studying teacher experiences with online learning:

• Early interviews reveal new challenges and strategies

• Later interviews repeat similar ideas (e.g., workload, engagement issues)

• When no new themes appear → saturation is reached

Alternative Concept: Information Power

A more modern approach is information power.

Information power means:

The richer and more relevant each participant’s data is, the fewer participants are needed.

Sample size depends on:

• Study aim specificity

• Participant relevance

• Quality of responses

• Use of established educational theory

• Strength of analysis

Factors That Influence Sample Size in Qualitative Education Research

1. Research Design

Different qualitative approaches require different sample sizes:

• Phenomenology: 5–15 participants

• Case study: 1–10 cases (with multiple data sources)

• Grounded theory: 15–30+ participants

• Narrative inquiry: 1–10 participants

• Qualitative descriptive studies: 10–25 participants

2. Depth of Data Collection Method

The method you use influences sample size:

• In-depth interviews → smaller samples

• Focus groups → moderate samples

• Open-ended questionnaires → slightly larger samples

• Observations + interviews → smaller samples due to richness

3. Homogeneity of Participants

Homogeneous groups (similar participants):

• Smaller sample size needed

• Example: middle school teachers in one district

Heterogeneous groups (diverse participants):

• Larger sample size needed

• Example: teachers across multiple grade levels and regions

4. Complexity of the Educational Phenomenon

More complex topics may require:

• More participants

• Multiple perspectives

• Different educational settings

Examples:

• Educational equity

• Technology integration across schools

• Leadership practices in diverse institutions

5. Practical and Ethical Constraints

Sample size may also depend on:

• Time available for data collection

• Access to schools or participants

• Ethical approval limitations

• Recruitment feasibility

Step-by-Step: How to Determine Sample Size in a Qualitative Education Dissertation

Step 1: Define the Educational Phenomenon

Clearly identify what you are studying.

Examples:

• Teacher burnout

• Student engagement in online learning

• Inclusive education practices

• Educational leadership experiences

• Classroom technology integration

Step 2: Choose a Qualitative Methodology

Your methodology shapes sample size expectations.

Common education methodologies:

• Phenomenology → lived experiences

• Case study → in-depth contextual analysis

• Grounded theory → theory development

• Narrative inquiry → personal stories

Step 3: Select Data Collection Method

Different methods affect saturation:

• Interviews → fewer participants needed

• Focus groups → moderate samples

• Open-ended questionnaires → slightly larger samples

Step 4: Use Data Saturation as the Primary Guide

During data collection:

• Monitor when responses become repetitive

• Track emerging themes

• Continue until no new insights appear

Step 5: Consider Information Power

Ask:

• Are participants highly relevant to the research question?

• Is the study narrowly focused?

• Is the interview guide detailed and focused?

Higher information power → smaller sample size needed.

Step 6: Review Similar Education Dissertations

Look at prior studies to:

• Identify typical sample sizes

• Justify your methodological decision

Step 7: Justify Sample Size in Your Dissertation

In Chapter 3, clearly explain:

• Why the sample size is appropriate

• What guided your decision (saturation or information power)

• How you determined when to stop collecting data

Example Justification Statement:

The sample size of 12 participants was determined based on the principle of data saturation, which was achieved when no new themes emerged from teacher interview data.

Typical Sample Size Ranges in Qualitative Education Research

Methodology	Sample Size Range
Phenomenology	5–15 participants
Case study	1–10 cases
Grounded theory	15–30+ participants
Narrative inquiry	1–10 participants
Qualitative descriptive studies	10–25 participants

Common Mistakes in Determining Sample Size

Avoid:

• Using statistical formulas (not appropriate for qualitative research)

• Fixing sample size too early

• Ignoring data saturation

• Choosing arbitrary numbers without justification

• Over-recruiting without added insight

Strengths of Smaller Qualitative Education Samples

• Rich, detailed educational insights

• Deeper understanding of teaching and learning

• Strong thematic development

• More meaningful interpretation

• Better alignment with qualitative goals

Final Thoughts on How to Determine Sample Size for a Qualitative Education Doctoral Dissertation

Determining sample size in a qualitative education doctoral dissertation is about depth, meaning, and conceptual completeness, not numbers alone. The most accepted approach is data saturation, supported by information power and strong methodological justification.

A well-written dissertation clearly explains how sample size was determined and demonstrates that enough participants were included to fully understand the educational phenomenon being studied.

If you need help with your methodology, consider dissertation editing! To learn more about us, please visit our website.