Stat in Psychology

Question

Assume your class took a final exam in psychology in which the scores produced a normal curve with a mean score of 80 and a standard deviation of 5.

1. 68% of the scores on the final exam would fall between____________and___________.

1. If the student scores within two standard deviations from the mean, what is the possible range of the student’s scores?

1. What percentage of students may have scored either higher than 85 or lower than 70?

Answer 1

Your first step here is to ask yourself what a standard deviation means. A standard deviation describes the spread of a large set of data, or in other words, describes how fat/skinny the bell curve is. Additionally, a standard deviation refers to the fact that 68% of scores will fall under ONE standard deviation (or 5 points above/below the mean). Therefore, you know that 68% of scores will fall between 75 and 85.

What percentage of scores fall within two standard deviations of the mean? The answer to that is always the same: 95%!

Two standard deviations means 2 x 5 because we know one standard deviation is 5 points. 95% of scores thus fall between 70 (which is 10 below your mean of 80) and 90 (10 points above your mean).

You should probably commit to memory what percentage of a data set falls within 1,2 and 3 standard deviations.