In statistics, various measures help us understand the position of a particular value within a data set. These measures of position include percentiles, quartiles, and deciles. Now, let's analyze each option provided:
1. Ninth decile:
- A decile is a measure of position that divides a data set into 10 equal parts. The ninth decile represents the value below which 90% of the data falls. Therefore, the ninth decile is indeed a measure of position.
2. Standard deviation:
- Standard deviation measures the dispersion or variability of a data set. It indicates how much the individual data points deviate from the mean of the data set. Standard deviation is not a measure of position; it is a measure of dispersion or spread.
3. First quartile:
- Quartiles divide a data set into four equal parts. The first quartile (Q1) represents the value below which 25% of the data falls. Thus, the first quartile is a measure of position.
4. 90th percentile:
- Percentiles divide a data set into 100 equal parts. The 90th percentile represents the value below which 90% of the data falls. Hence, the 90th percentile is a measure of position.
From this analysis, we can conclude that the standard deviation is the one that is not a measure of position. Instead, it is a measure of dispersion.
So, the correct answer is:
Standard deviation
