CASPer Z-Score Explained: What Programs See vs Your Quartile

What a CASPer z-score is

A z-score is a standard way to compare one result with a group. It answers one question: how many standard deviations is this score from the group average?

z = (your score − pool average) ÷ standard deviation of the pool

So a z-score of +1 means your score was one standard deviation above the average, −0.5 means half a standard deviation below it, and 0 means exactly average. Because it is relative, a z-score tells you nothing about how many answers were “correct”. CASPer has no correct answers to count.

Acuity's quartile article confirms the approach: it says CASPer is rated and z-scored relative to the strength of your peers' responses, which is why your quartile can shift between tests if the applicant pool changes.

How Acuity builds the score

Acuity's scoring explanation describes the steps:

1. Each question is rated on its own. Both questions in a scenario go to the same rater, who sees the full context, but each one gets its own rating.
2. Different raters see different scenarios. No rater scores you more than once. See who grades CASPer for how raters are trained and checked.
3. Ratings are averaged. Typed and video responses are combined into one overall score.
4. The result is standardized. The averaged scores are standardized to show each applicant's relative ranking within the pool.

The comparison pool matters. Acuity's country article says you are evaluated against applicants to programs in the same country, by raters from that country, and results cannot be transferred between countries. Scores are also tied to one test type, so a Canadian Casper 2 result is not compared with a United States Casper 1 pool. For test types, see CASPer 1 vs CASPer 2.

Converting a z-score to a percentile and quartile

Acuity does not publish the exact shape of the CASPer score distribution. If scores roughly follow a bell curve, which is a common assumption for standardized scores, z-scores map to percentiles like this. Treat the table as an illustration of the maths, not an official conversion chart.

Two things follow from this. First, the quartiles are wide: everything from roughly z = +0.67 upward is “4th quartile”. Second, small score differences near a boundary can change your quartile. Acuity gives the example of scoring at the 74th percentile on one test and the 76th on another, which places you in different quartiles even though the scores are almost identical. For what each band means in practice, see our CASPer percentile guide.

How programs use the standardized score

According to Acuity's score disclosure article, programs receive a single combined number with no breakdown by topic or competency, and each program decides how to use it. The same score can be more competitive at one program than another.

Published research shows z-scores in use. A 2024 anesthesiology residency study reported CASPer results as z-scores for 1,245 applicants. A 2026 physician assistant program study tested a hypothetical cut score set one standard deviation below the mean (z = −1) and found it would have removed 16.5% of applicants. That study is a simulation at one program, not a rule other programs follow.

In general, programs use CASPer to screen early, decide interview invitations or help rank applicants, often weighted alongside grades. Check each program's own published policy; our guide to how much CASPer matters and school pages such as McMaster's CASPer use cover specific cases.

What a negative CASPer z-score means

A negative z-score only means your overall score was below the average of your pool. It is not a fail; Acuity says CASPer is not a pass-or-fail test. Roughly half of any pool sits below average by definition, and Acuity notes that the pool includes many high-calibre applicants.

You will not see your z-score. Your quartile result tells you the band you landed in, typically around four to five weeks after your test. If you are in the lower bands and need to retest in a future cycle, our low-score recovery plan explains what you can work on.

What you can actually change

Because the score is relative, you cannot control the pool. You can control the substance of each answer: a clear decision, reasons, the perspectives of the people involved and a next step. Acuity's quartile article says higher-quartile applicants may explain their position fully, use the time available, consider all perspectives meaningfully and be familiar with the format.

Every question is rated separately, so one weak answer does not sink the rest. Treat each question as a fresh chance. For what a high-scoring answer contains, read what a 4th quartile answer looks like.

Sources and scope

Checked October 21, 2026 against Acuity's scoring explanation, quartile article, score disclosure article and country article, plus the published anesthesiology and physician assistant studies. The percentile table is a CasperCoach illustration that assumes a normal distribution; Acuity does not publish an official conversion. CasperCoach is independent of Acuity Insights.