GuidesResearch methodsWhat is self-selection bias & how can you avoid it?

What is self-selection bias & how can you avoid it?

Last updated

14 July 2023


Dovetail Editorial Team

Have you ever wondered why some studies seem to produce misleading or flawed results? Even though there are many reasons for this, one culprit could be self-selection bias. This is a common problem in research that occurs when participants choose to take part in a study rather than being randomly selected.

Self-selection bias can lead to a skewed sample that does not accurately represent the population as a whole. Luckily, there are ways to identify and minimize this bias in your research.

What is self-selection bias?

Self-selection bias occurs when participants voluntarily choose to participate in a study or program group rather than being randomly selected into one. This can lead to a biased sample that may only represent part of the population, as those who choose to participate may differ systematically from those who do not. 

For example, more motivated people with more free time or interest in the studied topic may be more likely to participate. This bias can significantly skew results and lead to inaccurate conclusions, especially if the sample size is small or if the bias is not recognized and addressed. As such, self-selection bias is a critical concern in research and must be taken into account to ensure the validity and reliability of the results.

Why is self-selection bias a problem?

Self-selection bias can result in a distorted or inaccurate view of reality. When individuals choose to participate in a study group, they’re more likely to have specific characteristics that make them different from the rest of the population. This can lead to a biased sample that doesn’t accurately reflect the population as a whole. 

For example, suppose a study on the effectiveness of a new diet plan only enrolls people who are already health-conscious. In that case, the results may not apply to the general population, as they may not be as motivated to follow a diet plan. This can lead to incorrect conclusions, recommendations, and decisions that may have negative consequences. 

Therefore, it’s critical to be aware of self-selection bias and take measures to minimize its impact to ensure that research findings are based on reliable and representative data.

What are the types of selection bias you should be aware of?

There are various types of selection bias to be aware of, including selective survival, observer bias, and volunteer bias. Each type of bias can have unique consequences for research studies and must be considered when interpreting results.

1. Selective survival

Selective survival bias occurs when certain individuals or groups are more likely to survive or continue in a study, leading to a biased sample. This can be a particular concern in longitudinal studies, where participants may drop out or researchers can’t reach them to follow up. 

For example, a study of the effectiveness of a new drug is conducted over a long period. In that case, participants who drop out due to adverse effects may differ from those who continue, leading to a biased sample.

2. Observer bias

Observer bias, or experimenter bias, occurs when the researcher's expectations or beliefs about the study's outcome influence their observations or interpretations. This can result in a biased sample that doesn’t accurately reflect the reality of the situation. 

For example, a manager's perception of employee performance may be biased by their personal relationship, causing them to rate their friend more favorably than another employee.

3. Volunteer bias

Volunteer bias occurs when individuals self-select to participate in a study group, leading to a sample that may not represent the entire population. This bias can result in skewed results if the participants who choose to participate differ systematically from those who do not. 

For example, a study on the effectiveness of a new exercise program only enrolls people who are already physically active. The results may not apply to the general population, as they may not have the same motivation to exercise.

What are the methods of reducing self-selection bias?

Self-selection bias can pose a significant challenge to the accuracy and reliability of research findings. Fortunately, there are several methods that researchers can use to reduce the impact of this bias. They include the following:

  • Use random sampling techniques to select participants. This will help you ensure the sample is representative of the population.

  • Offer incentives to encourage participation, attracting individuals who might not otherwise have volunteered. Incentives can include money, gift cards, or prizes.

  • Conceal information about the study from participants or researchers, using blinding techniques to reduce the influence of expectations and biases on the outcome.

  • Carefully consider the study design and the questions being asked to minimize potential sources of bias.

  • Recruit a large sample size, which can help to increase the sample’s diversity and reduce the impact of outliers.

  • Conduct sensitivity analysis to assess the impact of potential sources of bias on the results. Sensitivity analysis uses multiple what-if scenarios about the potential sources of bias to model a range of possible outcomes. 

  • Ensure that the study is conducted in a consistent and standardized way to reduce the impact of extraneous variables.

By employing these methods, researchers can help to minimize the impact of self-selection bias and produce more accurate and reliable results. This can lead to a better understanding of the phenomena being studied and inform decision-making in a variety of fields.

If you can't get rid of self-selection bias, you could decide to weight the results instead. This way, you give more weight to sample points less likely to have been included than to those likely to self-select.

An example of self-selection bias

Let's say a company is conducting a survey to determine the job satisfaction of its employees. However, the survey is emailed to employees, and participating is optional. The company's top-performing employees are more likely to complete the survey. This leads to self-selection bias, as the sample of respondents is not representative of the overall workforce.

As a result, the survey results may suggest that employee job satisfaction is higher than it actually is. The company may then make decisions based on inaccurate data. For example, the company may refrain from investing in initiatives to improve job satisfaction, thinking their employees are already highly satisfied. This could lead to decreased overall employee engagement and job satisfaction.


Self-selection bias can pose a significant challenge to the accuracy and reliability of research findings. However, you can produce more accurate and reliable results by understanding the different types of selection bias and employing methods to minimize their impact.

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