Your score on the exam is what we call a raw score. That score is meaningful when it is compared to a population of people that have similar characteristics to you, such as age, education and/or gender. A population with similar age, educaiton and gender has already taken each test and we compare your score to theirs. We do this by finding what percent of people in your population your score is better or worse than.
A Neurologist or a Neuropsychologist will take your full medical history into account and the patterb of results from all the tests in the exam to perform a diagnosis. They may also have your perform additional tests.
If your score is in the bottom 16th percentile for any test, we would recommend a follow up with a Neurologist or a Neuropsychologist.
Converting a raw score to a percentile uses basic statistical methods. Converting it using normative data involves comparing your test score to the scores of a representative sample of people who have taken the same test, in order to determine where your score falls in relation to the sample.
To do this, the raw score (the total number of points earned on the test) is first compared to the average score for the normative sample, which is typically represented as a mean and standard deviation. The standard deviation indicates how much variation there is in the scores of the normative sample.
Once the raw score has been compared to the mean and standard deviation of the normative sample, a percentile rank can be calculated. The percentile rank represents the percentage of people in the normative sample who scored at or below your raw score.
For example, if your raw score on a test is 75, and the mean score for the normative sample is 65 with a standard deviation of 10, then your score is one standard deviation above the mean (i.e., a z-score of 1). Looking up the corresponding percentile rank for a z-score of 1 in a standard normal distribution table, we find that the percentile rank is approximately 84.1%. This means that the individual scored higher than approximately 84% of the people in the normative sample.
Converting raw scores to percentile ranks using normative data is a common way of interpreting test scores, as it provides a meaningful way of comparing an individual's performance to that of a larger population.