# Ratio Statistics: Statistics

- Central Tendency
- Measures of central tendency are statistics that describe the distribution
of ratios.
- Median
- The value such that the number of ratios that are less than this value and the number of ratios that are greater than this value are the same.
- Mean
- The result of summing the ratios and dividing the result by the total number of ratios.
- Weighted Mean
- The result of dividing the mean of the numerator by the mean of the denominator. Weighted mean is also the mean of the ratios weighted by the denominator.

- Confidence intervals for PRB and measures of central tendency
- Displays confidence intervals for PRB, the mean, the median, and the weighted mean (if requested). Specify a value that is greater than or equal to 0 and less than 100 as the confidence level. The default setting is 95%.
- Dispersion
- These statistics measure the amount of variation, or spread, in the observed
values.
- AAD
- The average absolute deviation is the result of summing the absolute deviations of the ratios about the median and dividing the result by the total number of ratios.
- COD
- The coefficient of dispersion is the result of expressing the average absolute deviation as a percentage of the median.
- COV
- The coefficient of variation. The median-centered coefficient of variation is the result of expressing the root mean squares of deviation from the median as a percentage of the median. The mean-centered coefficient of variation is the result of expressing the standard deviation as a percentage of the mean.
- PRB
- The price-related bias. An index of whether assessment to price ratios are
systematically higher or lower for higher-priced properties. Regresses percentage differences in
assessment ratios from the median ratio on the base 2 logarithms of value proxy measures calculated
as the averages of sales prices and the ratios of assessed values to the median ratio. Gives the
percentage change in assessment ratios for a 100 percent change in value.
Refer to the following introductory video for a brief price-related bias overview:

- PRD
- The price-related differential, also known as the index of regressivity, is the result of dividing the mean by the weighted mean.
- Standard deviation
- The standard deviation is the result of summing the squared deviations of the ratios about the mean, dividing the result by the total number of ratios minus one, and taking the positive square root.
- Range
- The range is the result of subtracting the minimum ratio from the maximum ratio.
- Minimum
- The minimum is the smallest ratio.
- Maximum
- The maximum is the largest ratio.

- Concentration Index
- The coefficient of concentration measures the percentage of ratios that fall
within an interval. It can be computed in two different ways:
- Between Proportions
- Here the interval is defined explicitly by specifying the low and high values of the interval. Enter values for the low proportion and high proportion, and click Add to obtain an interval.
- Within Percentage of Median
- Here the interval is defined implicitly by specifying the percentage of the median. Enter a value between 0 and 100, and click Add. The lower end of the interval is equal to (1 – 0.01 × value) × median, and the upper end is equal to (1 + 0.01 × value) × median.

## Obtaining Statistics for Ratio Statistics

This feature requires the Statistics Base option.

- From the menus choose:
- In the Ratio Statistics dialog box, click Statistics.
- Select the statistics you want.