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Sample Size Calculation

Sample Size Calculation

Knowledge of the sample size is the first requirement to conduct random sampling or an experiment. The sample size is the total number of units, observations, or groups (in some cases) used to get the data to estimate a population parameter. As the name suggests, the sample size is that of the sample drawn from the population and differs from the population size.
The sample size for the given experiment or sampling effort is fundamental to any study design. Sample size decides the number of...

Systematic Sampling Method

Systematic Sampling Method

Sampling is a technique to select a portion (or subset) of the larger population and study that portion (the sample) to gain information about the population. Data are the result of sampling from a population. The sampling method ensures that samples are drawn without bias and accurately represent the population. Because measuring the entire population in a study is not practical, researchers use samples to represent the population of interest.
Systematic sampling is one of the simplest methods...

Convenience Sampling Method

Convenience Sampling Method

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Convenience sampling is a non-random method of sample selection; this method selects individuals that are easily accessible and may result in biased data. For example, a marketing...

Assumptions of Survival Analysis

Assumptions of Survival Analysis

Survival models analyze the time until one or more events occur, such as death in biological organisms or failure in mechanical systems. These models are widely used across fields like medicine, biology, engineering, and public health to study time-to-event phenomena. To ensure accurate results, survival analysis relies on key assumptions and careful study design.

Surveys

Surveys

Often, psychologists develop surveys as a means of gathering data. Surveys are lists of questions to be answered by research participants, and can be delivered as paper-and-pencil questionnaires, administered electronically, or conducted verbally. Generally, the survey itself can be completed in a short time, and the ease of administering a survey makes it easy to collect data from a large number of people.

Stratified Sampling Method

Stratified Sampling Method

Sampling is a technique to select a portion (or subset) of the larger population and study that portion (the sample) to gain information about the population. The sampling method ensures that samples are drawn without bias and accurately represent the population. Because measuring the entire population in a study is not practical, researchers use samples to represent the population of interest.
To choose a stratified sample, divide the population into groups called strata and then take a...

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Related Experiment Video

Updated: Jun 15, 2026

Problem-Solving Before Instruction (PS-I): A Protocol for Assessment and Intervention in Students with Different Abilities

Problem-Solving Before Instruction (PS-I): A Protocol for Assessment and Intervention in Students with Different Abilities

Published on: September 11, 2021

What is an adequate sample size? Operationalising data saturation for theory-based interview studies.

Jill J Francis¹, Marie Johnston, Clare Robertson

¹Health Services Research Unit, University of Aberdeen, Aberdeen, UK. j.francis@abdn.ac.uk

Psychology & Health

|March 6, 2010

Summary

This summary is machine-generated.

Establishing data saturation in theory-based interview studies requires clear principles. This research proposes a method using an initial analysis sample and a stopping criterion to determine when data saturation is reached, improving qualitative research rigor.

Related Experiment Videos

Last Updated: Jun 15, 2026

Problem-Solving Before Instruction (PS-I): A Protocol for Assessment and Intervention in Students with Different Abilities

Problem-Solving Before Instruction (PS-I): A Protocol for Assessment and Intervention in Students with Different Abilities

Published on: September 11, 2021

Area of Science:

Qualitative Research Methodology
Health Psychology
Sociology

Background:

Sample size justification in interviews often relies on 'data saturation,' but lacks standardized methods.
Theory-based interview studies pre-establish conceptual categories, yet saturation determination remains ambiguous.

Purpose of the Study:

To propose and demonstrate principles for establishing data saturation in theory-based interview studies.
To enhance the rigor and reproducibility of qualitative interview research.

Main Methods:

Proposed principles: 1) Specify an initial analysis sample size. 2) Define a stopping criterion for additional interviews without new data.
Demonstrated principles in two studies using the Theory of Planned Behaviour to identify belief categories.

Main Results:

Study 1 (retrospective): Achieved saturation for 'Normative' beliefs but not overall. Identified 84 shared beliefs among 14 general practitioners.
Study 2 (prospective): Achieved study-wide data saturation at interview 17. Identified 44 shared beliefs among 17 relatives regarding genetic testing for Paget's disease.

Conclusions:

The proposed principles provide a structured approach to determining data saturation in theory-based interview studies.
Specification of these principles is recommended for reporting qualitative research, with potential adaptability to other study types.