A practice test is accurate when the score it gives you is close to the score you earn on test day. That sounds simple, but most claims about "the most accurate practice test" online are a hunch, a sales line, or a single student's story. This page explains exactly how we measure it, so you can judge our numbers instead of trusting them.
The two numbers we report for every practice test
1. Bias: does it run high or low? Bias is the average gap between a practice score and the real score. If students average 505 on a provider's full-lengths and 511 on the real exam, that provider runs about 6 points low. Students usually call this "deflation." A test that runs low isn't broken. It just needs a conversion before you read it.
2. Spread: how much does it miss by? Spread is how far individual students land from the average gap. A test can run 5 points low on average but miss some students by 1 point and others by 12. A small spread means the test is predictable, even if it isn't calibrated. We report it as the typical miss in points (mean absolute error) and as the share of students who landed within 3 points.
A test with zero bias and a big spread is less useful than a test with a 5-point bias and a tight spread, because you can correct a known bias. You can't correct noise.
Where our data comes from
We use three sources, in this order of weight:
- Score reports submitted to us. Students send us their practice scores and their official score report. A data point counts only after we've seen the official report, and we never publish names or individual scores.
- Published research. Peer-reviewed studies and test-maker documentation, linked in each article.
- Public community compilations. Reddit and Student Doctor Network score spreadsheets. We use these to cross-check, not as proof, because they carry the biases below.
The biases we correct for
- Self-reporting bias. People who did well are more likely to post. Public MCAT spreadsheets have average real scores far above the national average, so their gaps may not hold for every scorer. We report the score range our data covers and warn when you fall outside it.
- Practice effect. Students take third-party tests early and official tests late. Some of the "deflation" is just studying. We compare tests taken within the same window where we can, and say so when we can't.
- Small samples. We publish the number of data points next to every figure. Under 30 data points, we label a number "early estimate."
- Old test versions. Providers rewrite tests and change scaling. We date every figure and re-check it each testing year.
What we will never do
- Accept payment, free access, or affiliate commission from a provider in exchange for coverage. We have no affiliate links.
- Publish a conversion without its sample size and date.
- Call any single score a prediction. A practice score narrows the range you're likely to land in. It doesn't tell you your number.
How to read an accuracy figure on our site
Every accuracy figure on TestPrep Advice follows the same pattern: the provider, its average gap with a sign (+ means real scores ran higher), its typical miss, the number of data points, and the date range. A hypothetical example: "Provider X: real scores averaged +4 points higher (typical miss ±3, n = 120, 2025–2026)." (This example is illustrative, not real data.)
Read the series
- Which MCAT Full-Lengths Predict Your Real Score?
- Are DAT Booster and DAT Bootcamp Practice Tests Harder Than the Real DAT?
- OAT Booster vs the ADA Practice Test: How Close Is the Calibration?
- LSAT PrepTest Scores vs Real Scores: How Much Do Students Drop?
Have a practice-vs-real score set to share? Send us a direct message on Instagram with your practice scores and a screenshot of your official score report. Every verified report improves these numbers for the next student.