Final answer:
A difference of less than 1.5 standard deviations between the lowest and highest index scores typically means the scores are within the normal range, suggesting consistency and low variability.
Step-by-step explanation:
If the difference between the lowest index score and the highest index score is less than 1.5 standard deviations, this generally indicates that the scores are within the normal range. Standard deviation is a measure of the dispersion of scores within a set of data. For example, in IQ testing, a standard deviation is typically 15 points, so an IQ score within one standard deviation above or below the mean (between 85 and 115 if the mean is 100) is considered average. Therefore, a difference that is less than 1.5 standard deviations would still fall within this normal range category. When dealing with various types of assessments, this degree of dispersion suggests that the set of scores is relatively consistent with each other and that there is not a high level of variability or inconsistency.