The *trimean* is an estimate of central tendency, and is calculated as a weighted average of the median and the two quartiles of a set of values.

The formula for trimean is *(quartile1 + median * 2 + quartile3) / 4*. Trimean is considered a robust statistic, and is therefore less sensitive to outliers in the data.

### Example

Given the values [5,10,15,20], the statistics are:

- Quartile1 =
**7.5 = (5 + 10) / 2**
- Median =
**12.5 = (10 + 15) / 2**
- Quartile3 =
**17.5 = (15 + 20) / 2**
- Trimean =
**12.5 = (7.5 + 12.5 + 12.5 + 17.5) / 4**