Health and Psychology

I’m teaching psychological assessment and it’s finals week. That means I’m explaining a lot about psychological test scores and how to evaluate them. Most psychological tests are based on the normal curve (pictured below). The normal curve is a statistically way of looking at a phenomena in a population that is believed to be normally distributed, like IQ scores. The midpoint in the distribution is referred to as the mean. This is a fixed number.

There are various rating scales that are used when discussing the normal curve. These are Z scores, Index scores, T scores, Stanines, and Scaled Scores. The method to look at how spread out the scores are is called the Standard Deviation. One standard deviation from the mean is the average range.

So an IQ score with a mean of 100 and a standard deviation of 15, means that average scores will fall within scores of 85 to 115. T Scores with a mean of 50 and a standard deviation of 10 will have average scores between 40 and 60. Z scores with a mean of zero and a standard deviation of 1 will have an average range of -1 to +1. A scaled score with a mean of 10 and a standard deviation of 3 means that scores between 8 and 12 are in the average range. A score of 7 is below average and a score of 13 is above average.

Scores are transformed to fit into a normal distribution to be able to better compare them. Another way to compare scores is through percentile rank. A percentile rank is the percentage of the population that score is above. So a percentile rank of 50 means that person is in the middle of the population and does equal to 50% of their peers. A percentile rank of 16 means they perform as well as only16% of their peers.

This helps people when looking at test scores to understand what they mean about an individual.  If you want to know what test scores mean feel free to contact me.