Surveys help you collect participants’ views about a concept, product, or service. But if your survey isn’t measuring what you designed it to measure?

Reliability testing in survey research verifies if respondents understand your questions and can provide accurate and objective responses. 

Let’s explore reliability testing, types, and strategies to help you improve your survey reliability.

Understanding Reliability in Survey Research

Reliability refers to the degree to which your measurement method is consistent and stable over time. This means that if you use a reliable measurement method, you should get the same results when you repeat measurements under the same conditions.

Reliability is essential for obtaining accurate data that reflects the reality of your research topic. For example, if you have a survey that consistently gets similar answers from people over time, it indicates the research method is reliable and a good way of measuring the concept you’re trying to measure.

Validity isn’t the same thing as reliability; validity is the accuracy of your measurement method. 

Keep in mind that a method can be reliable without being valid, but it cannot be valid without being reliable. For example, if you weigh yourself on a broken scale, you can get the same number every time (reliable), but it will not match your genuine weight (invalid).

Depending on what you’re trying to measure and how you’re measuring it, there are different kinds of reliability you can look for in your survey. Here are some of the most common types of reliability: test-retest, internal consistency, and inter-rater reliability.

Test-Retest Reliability

This assesses the consistency of results when the same test or questionnaire goes out to the same sample at different points in time.  This type of reliability is used when you expect the phenomenon you are measuring to be stable over time, such as intelligence or personality traits.

Steps to Assess Test-Retest Reliability

  • Select a Representative Sample

You need to choose a group of people who are similar to your target population and who can take your survey twice without changing their answers significantly.

  • Identify Appropriate Time Intervals to Administer the Surveys

You need to pick a time interval that allows your sample to complete the survey multiple times without significantly changing their answers. So, the interval shouldn’t be too short or too long.

  • Calculating Correlation Coefficients

Next, you need to compare the scores of your survey from the first and second administrations. The standard way to do this is by calculating the correlation coefficient- it is a number between -1 and 1.

The correlation coefficient indicates how closely related two sets of data are; a higher correlation coefficient means higher test-retest reliability. The most common method of calculating the correlation coefficient is the Pearson correlation coefficient (r). 

Here’s the formula: r = (Σ(X₁ – X̄)(X₂ – Ȳ)) / √(Σ(X₁ – X̄)² * Σ(X₂ – Ȳ)²)
Where X₁  and  X₂  are the first and second survey administration scores respectively

X̄ is the mean of X₁, and Ȳ is the mean of X₂.

Plug the values from your data into the formula, and you’ll get the correlation coefficient.

  • Interpreting Test-Retest Reliability Results

You must assess the correlation coefficient to see if it meets your standards for acceptable reliability. Generally, 0.7 or higher is considered to be good test-retest reliability, but this can vary depending on your survey research field and goal.

  • Addressing Potential Sources of Error and Bias

Finally, identify and reduce any factors that may impair your survey’s test-retest reliability, such as unclear questions, different testing settings, or changes in sample characteristics.


Internal Consistency Reliability

Internal consistency reliability is a way to assess how well a test measures a single construct or trait. It is important because it shows if the trait or concepts are related to each other and form a coherent scale or index.

Commonly Used Measures of Internal Consistency Reliability

  1. Cronbach’s Alpha Coefficient

Cronbach’s alpha is a statistic that goes from 0 to 1 indicating how well test items are associated with one another. A higher alpha value shows greater internal consistency and reliability.

  1. Split-Half Reliability

Split-half reliability compares the scores of each half of the test items. If there’s a strong correlation between the two halves, it indicates a high internal consistency reliability.

How to Analyze and Interpret Internal Consistency Reliability Results

First, you need to compare the obtained values from Cronbach’s alpha or split-half reliability with some benchmarks or criteria. For example, some researchers suggest that an alpha value of 0.7 or above is acceptable for most purposes, while others may have different standards. 

You also need to consider the nature and purpose of your test, the number and difficulty of the test items, and the characteristics of your sample.

Techniques to Enhance Internal Consistency Reliability

  • Item Analysis

Item analysis is a process that examines the performance of each test item and its relationship with the overall test score. 

  • Identifying and Removing Problematic Items

You can also identify items that are too easy or too hard, or that have low or negative correlations with the other items or the total score. Identifying and removing problematic items increases the homogeneity and validity of the test.


Inter-rater Reliability

Inter-rater reliability is a measure of how well two or more raters agree on the same thing. It shows the quality and consistency of the data collected. 

Applications of Inter-Rater Reliability in Survey Research

This means assigning codes or categories to images or text when analyzing them. For example, you may categorize news stories as favorable, bad, or neutral. Inter-rater reliability indicates how closely the items agree on the codes or categories they assign.

  • Observational Studies

Inter-rater reliability is a measure of how much agreement there is between the observers on what they’re seeing and recording. It is a study of behaviors or events that you observe and record.

To do an effective observational study, it’s important to have a clear idea of what you’re looking at and how you’re recording it. For example, you could see how many times students raise their hands in a class.

Methods to Assess Inter-Rater Reliability

  • Cohen’s Kappa Coefficient

This is a statistic that compares the observed agreement between raters to the expected agreement by chance. It goes from -1 to 1, with 1 indicating perfect agreement, 0 indicating no agreement, and negative values indicating worse-than-chance agreement.

For example, if two raters code 100 polls as positive or negative, and they agree on 80 of them, their observed agreement is 80%. But if they would agree on 50 of them by chance, their expected agreement is 50%. Their kappa coefficient is (0.8 – 0.5) / (1 – 0.5) = 0.6, which indicates moderate agreement.

  • Intraclass Correlation Coefficient (ICC)

It measures the consistency of ratings among raters. It also ranges from -1 to 1, where 1 means perfect consistency, 0 means no consistency, and negative values mean negative consistency. 

For example, if two raters rate 7 products on a scale of 1 to 7, and their ratings are very similar, their ICC will be close to 1. But if their ratings are very different, their ICC will be close to 0 or negative.

How to Ensure Consistent Coding and Interpretation Among Raters

  • Define the codes or categories clearly and provide examples
  • Train the raters on how to apply the codes or categories
  • Provide feedback and check for errors
  • Calculate inter-rater reliability and resolve any disagreements


Factors Affecting Reliability in Survey Research

  • Sample Characteristics and Representativeness

The sample size should be reasonably large and representative of the population under consideration. If the sample is too small, biased, or not randomly selected, the results may not be generalizable or replicable.

  • Survey Design and Question-Wording

The survey questions should be clear, relevant, and unbiased. They should also be consistent with the research goals and hypotheses. 

If the questions are vague, confusing, leading, or loaded, they may influence the respondents’ answers or cause them to skip questions or abandon the survey.

  • Administration Procedures and Timing

Design a standardized and ethical method to administer the survey; use the same guidelines and procedures for all participants. The timing should also be appropriate to the topic and respondents’ availability.

If the survey is administered sporadically, unethically, or at an inconvenient time, it may affect the response rate, quality, and validity.

  • Rater Training and Calibration

When using human raters or observers, they should be trained and calibrated to ensure interrater reliability. This means they should apply the same criteria and processes when rating or observing the same phenomenon.

There is a high likelihood of untrained, inexperienced, or inconsistent raters may introduce errors or biases into the data.

Read Also – Questionnaire Design: 10 Questioning Mistakes to Avoid


Strategies to Improve Reliability in Survey Research

Pilot testing involves a small-scale trial with a sample of respondents similar to the target population, while pre-testing involves a more detailed examination of the survey instrument and procedures with a few respondents or experts.

You can use pilot and pretesting to figure out if there’s anything wrong with the questions, how they’re phrased, or how they make sense. It can also help you to fix any technical or logistic problems with the survey method or how it’s delivered.

Use simple and familiar words, avoid leading questions, use specific and concrete terms, avoid jargon or technical terms, and provide clear definitions or examples when necessary.

  • Standardized Administration Protocols

These rules and processes help make sure the survey is done consistently and consistently across all respondents and different settings. They help reduce the amount of variation and mistakes that could come from different interviewees, methods, or situations.

Standardized administration protocols include scripted introductions and instructions, training and monitoring interviewers, using consistent question sequences and wording, and minimizing external influences or distractions.

  • Rater Training and Inter-Rater Agreement Sessions

Rater training is when the raters are given clear instructions and examples on how to evaluate the answers or data. Inter-rater agreements are when the raters compare and discuss each other’s ratings to resolve any issues or disagreements.

This ensures that the raters have a common understanding of the rating criteria and apply them consistently and accurately. 


Reliability testing is a continuous process that requires thoughtful planning and implementation You also have to carefully select the type of reliability test that fits your research goals.

It allows you to determine the consistency and accuracy of your data collection methods. This helps you to identify and avoid errors or biases that can negatively affect your data quality and credibility.

  • Moradeke Owa
  • on 8 min read


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