Ideally, a respondent’s answer should remain consistent over time, regardless of how many times they complete the survey. But factors like response bias and question misinterpretation influence respondents’ answers, causing them to respond differently on different occasions.

The test-retest reliability helps you determine the consistency and accuracy of survey data over time. If a survey’s test-retest reliability is low, it could mean the survey questions aren’t very specific, reliable, or consistent.

Let’s explore why test-retest reliability is important in surveys and ways to optimize it.

Definition and Explanation of Test-Retest Reliability

The test-retest reliability of a survey is a measure of how consistent the results are over time. It is calculated by administering the same survey to the same group of people at two different points in time and comparing the results.

The greater the correlation between the two sets of scores, the higher the test-retest reliability. The goal of this test is to assess whether the survey measures what it’s intended to measure and determine if the results are reliable over time.

Here’s an example of test-rest reliability in a survey: you create a survey to assess your customer satisfaction with a new product, then distribute it to a sample of your customers. Next, track their responses and compute an average satisfaction score.  

After a month, you send the same survey to the same customers and collect their responses again. Next, compare the average satisfaction scores from the first and second surveys, if they are close, your survey has high test-retest reliability.

But if you notice a significant difference in the average satisfaction score between the first and second surveys, your survey has low test-retest reliability.

Factors That Affect Test-Retest Reliability

1. Types of Questions in Surveys

Different types of questions may elicit different responses from the same respondents over time. For example, open-ended questions can make room for more variation in responses than closed-ended questions.

Highly sensitive or emotionally loaded questions may also cause varied responses based on the respondent’s mood or situation at the time of the survey. Vague, ambiguous, or complex questions also typically lead to inconsistent responses.

Read More: Bad vs Good Survey Questions + [11 Examples]

1. Time Interval Between Tests

Short test intervals such as weeks or a month tend to result in higher reliability because the likelihood of changes in respondents’ attitudes or conditions is low. However, testing the same individuals twice in a matter of hours may result in response bias or fatigue, which can reduce reliability. 

Also, if you administer the same survey or test twice over a long period (e.g., a few months or years), you can expect low test-retest reliability. Several factors can affect respondents’ opinions or abilities such as learning, experience, mood, motivation, and others.

       2. Variability of Respondents

Respondent variability refers to how different or similar your respondents are in terms of personality traits, backgrounds, beliefs, and behaviors. The degree of variability can influence how much variation or consistency there is in the responses over time.

For example, if you have a highly variable group of respondents (e.g., people from different ages, genders, cultures, etc.), you may expect to see low test-retest reliability, because they may have different perspectives or reactions to the same questions over time.

However, if you have a highly homogeneous group of respondents (e.g., people from the same age group, gender group, culture group, etc), you may expect to see high test-retest reliability. This is because they may have similar perspectives or reactions to the same questions over time.  

So, it’s best practice, to select a representative sample of respondents that reflects the population you want to study.

Methods to Improve Test-Retest Reliability

1. Use of Standardized Questionnaires

Standardized questionnaires allow you to compare different studies or populations while minimizing varying responses. They have clear instructions, fixed response options, and consistent scoring methods that reduce variability and ambiguity in test results.

For You: 4 Types of Questionnaires + Free Question Examples

2. Ensuring Consistency in the Administration of Surveys

Use the same mode of delivery (e.g., online, paper, phone), environment, time, and interval for all participants. You should also avoid any external factors that could affect the participants’ mood, motivation, or concentration, such as noise, distractions, or incentives.

If you are conducting physical surveys, train survey administrators to follow a standardized survey administration protocol; instructions on how to read questions and respond to participant inquiries.

3. Use of Pretests and Pilot Testing

Pretests and pilot testing allow you to assess the test’s reliability and validity by checking the quality and clarity of the survey. The survey is usually given to a small sample of respondents before the main survey, which helps you identify errors or potential problems in the questionnaire.

You can use feedback from pretests and pilot testing to revise and improve your test before using it with your target population.

Applications of Test-Retest Reliability in Survey Research

1. Evaluation of Questionnaire Design

Test-retest reliability can help you assess how well your questionnaire is designed and whether it measures what you intend to measure.

This information can be used to refine the survey instrument, improving its validity and reliability. Revise your questionnaire to make it more clear, valid, and reliable, if you see significant discrepancies in the results.

2. Monitoring Changes in Attitudes or Behaviors Over Time

Test-retest reliability can help you track how your sample reacts to specific events or interventions over time. A significant difference indicates that one or more factors influenced the behavior or attitudes of your sample.

3. Assessing the Effectiveness of Interventions or Treatments

Test-retest reliability can help you see how an intervention or treatment affects the attitudes or behaviors of your sample. If you don’t see a significant, you can conclude that the treatment or intervention was successful.

Limitations of Test-Retest Reliability in Surveys

1. Practice Effects and Respondent Fatigue

Practice effects and respondent fatigue refer to the changes in respondents’ behavior or motivation that can occur when they take the same survey more than once. 

Respondents may become more familiar with the questions and answer them more quickly or accurately the second time. They could also get bored or tired and answer them less carefully or honestly. 

Learn More –  Survey Fatigue: Meaning, Causes & Mitigation 

2. Environmental Factors That Can Affect Responses

Participants’ responses can be influenced by the context or setting they complete the survey. The difference in weather, news, emotions, social interaction, or personal experiences between the survey’s first and second surveys can alter respondents’ opinions.

Changes in the physical environment, such as noise, distractions, or interruptions, can also have an impact on participants’ concentration and engagement. These factors can introduce random or systematic errors in the responses, reducing the survey’s test-retest reliability.

3. The Role of Memory in Test-Retest Reliability

This is how well respondents recall and are consistent with their previous answers. Their ability to recall past responses accurately may deteriorate over time, introducing errors in their retest responses.

For example, respondents may forget some of their answers or change their opinions or preferences over time. They could also try to recall their answers and repeat them exactly, or give entirely different answers.

Conclusion

Test-retest reliability indicates how reliable data collected from the same respondents at different time points are, and how to improve it. It also helps you identify factors influencing the change in responses and improve your survey design.

But test-retest reliability has its limitations. You need carefully ensure that all the factors between the first and second surveys remain the same, and eliminate biases that may trigger different responses.