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Calculate your ideal sample size

Last updated

11 May 2023

Author

Dovetail Editorial Team

If you're planning to conduct a research study or survey, one of the most critical factors to consider is the sample size. A small sample size can result in unreliable results, while a large sample size can waste resources and time. Therefore, calculating your ideal sample size is crucial to ensure your study provides reliable and valid results.

Whether you're conducting market research, medical trials, or social science studies, understanding how to calculate your ideal sample size is essential for a successful research project.

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What is a sample size?

The sample size is the number of participants or data points a researcher needs to collect to make inferences about a larger population. Researchers use sample size to conclude a population. 

For example, if a researcher wants to know the average height of adult males in the United States, the population would be all adult males in the US. The researcher would collect a sample of adult males, measure their height, and use this information to estimate the average size of all adult males in the US. 

Understanding sample size

Comprehending sample size is vital for conducting meaningful research that provides reliable and accurate results. Here are some key concepts that can help you better understand this critical aspect of research:

Representativeness

A sample is considered emblematic if it accurately reflects the population characteristics from which it’s drawn. To ensure representativeness, researchers should use appropriate sampling methods, such as random or stratified sampling.

Confidence level

This is the degree of certainty the results obtained from a sample accurately represent the population. A confidence level of 95% means there is a 95% chance the population parameter falls within the confidence interval.

The margin of error

The margin of error is the sampling error expected in the results due to using a cross-section instead of the entire population. 

Power

This refers to the ability of a study to detect an actual effect—if it exists. A study with high power has a greater chance of detecting a significant impact, while a study with low power may fail to see the effect, even if it exists.

Effect size

This is the magnitude of the difference between groups or the strength of the relationship between variables. The larger the effect size, the stronger the relationship.

By selecting an appropriate sample size, researchers can ensure their findings represent the population being studied and have the necessary level of precision and confidence.

Does having a statistically significant sample size matter?

A statistically significant sample size is the minimum number of participants required to detect a meaningful difference in the studied population. Statistical significance doesn't guarantee the validity or importance of the study results. 

However, it provides evidence that the observed differences in the sample are unlikely coincidental. Therefore, a statistically significant sample size is vital in drawing valid conclusions and making informed decisions based on the study results.

How to calculate sample size

Quantifying the ideal sample size requires careful consideration of several factors, including the research question, the desired accuracy, and the confidence level. Here's a general overview of how to calculate sample size:

Power analysis is a statistical method used to determine the ideal sample size based on the effect size, the significance level, and the study's desired power. 

Confidence intervals are an analytical method used to estimate the range of values probable to contain the actual population variable with a certain confidence level. 

The margin of error is a demographic method used to gauge the scope of values likely to have the true population parameter with a certain precision level. 

The sample size calculation may differ depending on the statistical method and study design.

Sample size calculator

Maximize your research’s impact with the right sample size and get an accurate representation of your target audience.

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Sample size


The total number of people whose opinion or behavior your sample will represent.

The probability that your sample accurately reflects the attitudes of your population. The industry standard is 95%.

The range (measured as a percentage) that your population’s responses may deviate from your sample’s.

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Sample size

Sample size formula

The formulas for calculating sample size depend on the statistical method used. Here are the commonly used formulas:

Power analysis: N = [(Zα/2 + Zβ) / ES] ^ 2

Where:

N = sample size

Zα/2 = the critical value of the standard normal distribution for a specified level of significance

Zβ = the critical value of the standard normal distribution for a particular power of the study

ES = the effect size, representing the magnitude of the difference or effect the study tries to detect

Confidence intervals:  n = [(z * σ) / E] ^ 2

Where:

N = sample size

z = the critical value of the standard normal distribution for a specified level of confidence

σ = the standard deviation of the population

E = the desired margin of error

The margin of error: MOE = Z * (σ / √n)

Where:

Z = the z-score associated with the desired level of confidence (e.g., for 95% confidence, Z = 1.96)

σ = the standard deviation of the population

n = the sample size

Margin of error calculator

Optimize your research’s impact when you improve the margin of error.

0%

Margin of error


The total number of people whose opinion or behavior your sample will represent.

The probability that your sample accurately reflects the attitudes of your population. The industry standard is 95%.

The number of people who took your survey.

0%

Margin of error

These formulas are general guidelines, and researchers should consult with a statistician or use statistical software to ensure the sample size calculation is appropriate for their particular research question and study design.

FAQs

Is a larger sample size better?

Yes, a larger sample size is better. A larger sample size increases the statistical power of a study, meaning it's more likely to detect actual effects or differences between groups.

Why use a sample size calculator?

A sample size calculator is used to determine the optimal sample size needed to obtain reliable and valid results in a study. It considers several factors, including the desired level of statistical power, the expected effect size, and the significance level.

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