Introducing percentile scoring

We're updating our scoring methods

At TestGorilla, we’re committed to continually improving your experience and ease of use of our platform. Our next area of focus is aimed at strengthening our scoring methods and giving you more options than ever before. This article will cover the scoring method changes being made to the platform, and as we roll out these changes to more users our existing articles will be updated to include these new changes. This article applies to all new and current users of TestGorilla.

Approx. reading time 8 minutes

In this article

  1. What is changing?
  2. What are percentiles?
  3. Why percentiles?
  4. How are percentile scores calculated?
  5. Using percentile scoring
  6. Common questions

 

What is changing?

Starting on October 14th, and throughout the month, we’ll be rolling out percentile scoring across the app. If you’re a new user, you can use percentile scoring immediately! You’ll see how candidates rank against others who have taken the same assessment, giving you a clearer, more accurate way to evaluate results.


In addition, the following updates will be made:

  • There is a new toggle on each assessment page to switch between scoring metrics. Percentile is set as the default, but you can switch to “Raw score” (previously “Percentage”) if you prefer.
  • On each candidate's results page, percentile and raw scores appear side by side, along with a bell curve showing how they compare to others who took the same assessment.
  • Both scoring metrics are presented side by side in PDF reports for easy comparison.
  • Only the metric selected on the assessment page is available in CSV and Excel exports.

 

What are percentiles?

Percentiles are a scoring metric that helps you understand candidate performance compared to others. For example, a candidate scoring in the 54th percentile is a candidate who did better on the test than 54% of other candidates in our reference group test. Note that this is different from a candidate scoring 54% of correct answers on a test.

The alternative to percentile scoring is a percent correct score. To stick with our example, scoring 54% of correct answers simply means that the candidate answered a certain number of questions correctly. It doesn’t take into account the difficulty or similarity of those questions, which makes it much easier to overlook good candidates.

With a percent correct score, there’s no way to know whether the 54% is because the candidate did well on the important difficult questions, or because they aced all the easy questions that a highly skilled candidate might find distracting. Additionally, comparing results across assessments can be tricky with percent correct scores, as tests of the same skill across assessments will have different questions.

The percentile score is a single number that combines information about the candidate’s answers and question difficulty. This makes it easy to differentiate between good, great, and excellent candidates. It also enables you to compare candidates across different assessments, as the percentile score already weighs in the question and test difficulty. When a developer scores in the 90th percentile on a Javascript test, that means they showed better performance than 90% of other candidates who took it.

While a 90% correct score on a difficult test might mean a lot, a 90% score on an easy one doesn’t mean as much. A result in the 90th percentile always means the same – that a candidate is better than 90% of others who took the test. This makes it possible to rank and compare candidates without pondering the individual questions, their differences, and their difficulties.

 

Why percentiles?

There are several key factors as to why we have added percentile scoring:

  1. Consistent and reliable interpretation of results
  2. Accounts for question difficulty
  3. Increased confidence in a candidate’s skills
  4. Allows flexibility

For a more in-depth look into the science and reasoning behind each factor, check out our blog.

 

We believe percentile scores aren’t just a new way to rank candidates—they are a powerful tool that helps you make more informed, confident hiring decisions. Whether you’re evaluating individual tests or overall assessments, percentiles offer a more complete view of a candidate’s capabilities.

Percentile scores offer deeper insights by accounting for question difficulty, making it easier to compare candidates fairly across assessments, even if they face different levels of challenge in the test. Unlike percentage scores, which only reflect correct answers, percentiles show how well a candidate performs compared to others.

Example: A candidate in the 80th percentile performs better than 80% of other test-takers. This helps you distinguish between good, great, and exceptional candidates more clearly.


However, if a candidate scores 80% in one assessment, that is not equivalent to scoring 80% in a different assessment.


→ Even though it’s the same test, candidates are answering different sets of questions, with unequal difficulty.


If a candidate scores in the 80th percentile in one assessment, that is equivalent to scoring in the 80th percentile in another assessment.


→ Even though different questions were answered, the normalization algorithm accounts for question difficulty in calculating percentiles.



How are percentile scores calculated?

At the test level, we account for the difficulty of individual questions. Consider two candidates: one might answer easier questions correctly, while the other tackles harder ones. Our system adjusts their scores accordingly.

This is done by weighing the correct answers with the parameter describing the questions’ difficulty. Question difficulty is calculated by looking at the performance in the reference sample and calculating how likely it is for the average candidate to answer the question correctly.

A question with a 0.8 difficulty is a question that 80% of candidates can answer correctly, meaning that it is easy. A question with a 0.2 difficulty is a hard question, and only 20% of people can answer it correctly. This information is then used to give a higher “score” to the difficult question than the easy one.


For a more in-depth look into how percentile scores are calculated, check out our blog.

 

Using percentile scoring

With this update, there are several ways you can begin using percentile scoring in your hiring process immediately:

Toggle scoring methods

Percentile scoring will now be the default scoring method - this means that the candidate results in the assessment overview page will show up using the percentile scoring metric automatically. This can be toggled back to the raw score option if it better suits your needs.

Results page

On the results page for each candidate is a bell curve that marks the percentile the candidate falls into, compared to the average. Below the bell curve are the tests included in the assessment, which display both the percentile the candidate falls into for each test, as well as the raw score (percentage) they received. 

Note: Certain test results, such as for typing and personality tests, will retain their current display for the time being.

 

PDF reports

Both percentile scoring and raw scores will be visible within PDF reports. They are displayed side-by-side at both assessment and test levels. 

CSV/Excel exports

CSV and Excel exports will display a single scoring metric - whichever is selected in the assessment overview. This can be either percentile scoring or raw score.

Assessment summary PDF reports

The scoring metric chosen also affects how the results summary PDF report displays candidate performance across the assessment. Your chosen metric will be displayed across the entire report. If you want to change the displayed metric, simply adjust the toggle in the assessment overview.

 

Common questions

Can I still view the percent correct scores?
Yes! You can still view percent correct scores under the “raw score” option, but the default scoring will now be percentile-based.

Will this affect my existing assessments or data?
Your previous assessment data remains intact and will now be available under the "raw score" option. You will also see the percentile score in past test results.

How are percentile scores calculated?
Percentile scores take into account both the number of correct answers and the difficulty of the questions, showing how well a candidate performed compared to all other candidates who took the same test in TestGorilla.

These scores are derived from z-scores, which assume a standard normal distribution (i.e., bell curve). These z-scores are computed using statistics specific to each question, which adjusts for question difficulty. The z-scores are then converted into percentile scores to reflect the candidate’s ranking relative to others. For more details on how the calculation works, please visit the Science blog.

What is the difference between a percentile score and a percent correct score?

A percentile score compares a candidate’s performance to that of others who took the same test, showing how they rank against the reference group. A percent correct score simply reflects the number of questions answered correctly. You can view the percent correct (raw score) under the “raw score” option.

How do percentile scores benefit my hiring process overall?

 Percentile scores provide a consistent way to compare candidates because they show how well someone did compared to others, regardless of the test difficulty. Unlike raw scores, where scoring 60% on an easy test isn’t the same as scoring 60% on a hard test, percentiles reflect the candidate’s performance relative to their peers, making comparisons fair and standard over time.

Why should I trust percentiles more than percentage scores? 

Percentiles account for the performance of other candidates who took the same test and for the difficulty of each question, giving a clearer picture of a candidate’s skills relative to others. A high percentage on an easy test isn’t as informative as a high percentile score, which reflects the candidate’s standing among a broad reference group.

What is the reference group for percentile scores?

The reference group consists of all candidates who have taken the test, allowing you to compare your candidates to a global benchmark rather than just those within your immediate hiring pool.

How are difficult questions weighted differently from easy ones in the percentile calculation? 

Our system adjusts scores based on the difficulty of the questions. For example, answering a difficult question correctly (which few candidates can do) contributes more to the final score than an easy question.

How should I interpret a candidate scoring in the 90th percentile? 

A candidate in the 90th percentile performed better than 90% of other TestGorilla candidates who took the same test. This shows their relative strength compared to a broader talent pool.

Do candidate percentile scores change over time, when more and more candidates take the test? The data used to compute percentile scores are regularly reviewed and updated over time. The exact cadence of these updates is determined by several factors, including the number of candidates and the time since the last update.

What if I want to emphasize certain skills more than others in my assessment? 

You can assign different weights to tests within an assessment. The percentile score will adjust to reflect the relative importance you place on each skill area, providing a customized overall score.

Will the percentile score change if I add or remove tests from an assessment? 

Yes, the overall percentile score is recalculated based on the combination of tests and the weights assigned to them, ensuring that it reflects your specific hiring needs.

How can we seamlessly integrate percentile scores into existing workflows when we rely on an ATS (Applicant Tracking System) integration? 

You’ll be able to choose which scoring metric—percentile or raw score—you send to your ATS. For new ATS integrations, percentile scoring will be selected by default, but you can switch to raw scores if you prefer.

For existing ATS integrations currently using raw scores, this setting will remain unchanged unless you decide to switch to percentiles. If you do switch, all future candidate scores will be sent as percentiles, but previously sent scores will stay in raw score format and cannot be updated retroactively.

Please note, that this solution will be available within November. We’ll also provide clear guidance to help you make the switch and recommend using percentiles for better candidate comparisons.

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