This code system http://hl7.org/fhir/observation-statistics defines the following codes:
Code | Display | Definition |
average | Average | The [mean](https://en.wikipedia.org/wiki/Arithmetic_mean) of N measurements over the stated period |
maximum | Maximum | The [maximum](https://en.wikipedia.org/wiki/Maximal_element) value of N measurements over the stated period |
minimum | Minimum | The [minimum](https://en.wikipedia.org/wiki/Minimal_element) value of N measurements over the stated period |
count | Count | The [number] of valid measurements over the stated period that contributed to the other statistical outputs |
totalcount | Total Count | The total [number] of valid measurements over the stated period, including observations that were ignored because they did not contain valid result values |
median | Median | The [median](https://en.wikipedia.org/wiki/Median) of N measurements over the stated period |
std-dev | standard deviation | The [standard deviation](https://en.wikipedia.org/wiki/Standard_deviation) of N measurements over the stated period |
sum | sum | The [sum](https://en.wikipedia.org/wiki/Summation) of N measurements over the stated period |
variance | variance | The [variance](https://en.wikipedia.org/wiki/Variance) of N measurements over the stated period |
%20 | 20th percentile | The 20th [Percentile](https://en.wikipedia.org/wiki/Percentile) of N measurements over the stated period |
%80 | 80th percentile | The 80th [Percentile](https://en.wikipedia.org/wiki/Percentile) of N measurements over the stated period |
4-lower | lower quartile | The lower [Quartile](https://en.wikipedia.org/wiki/Quartile) Boundary of N measurements over the stated period |
4-upper | upper quartile | The upper [Quartile](https://en.wikipedia.org/wiki/Quartile) Boundary of N measurements over the stated period |
4-dev | quartile deviation | The difference between the upper and lower [Quartiles](https://en.wikipedia.org/wiki/Quartile) is called the Interquartile range. (IQR = Q3-Q1) Quartile deviation or Semi-interquartile range is one-half the difference between the first and the third quartiles. |
5-1 | 1st quintile | The lowest of four values that divide the N measurementsinto a frequency distribution of five classes with each containing one fifth of the total population |
5-2 | 2nd quintile | The second of four values that divide the N measurementsinto a frequency distribution of five classes with each containing one fifth of the total population |
5-3 | 3rd quintile | The third of four values that divide the N measurementsinto a frequency distribution of five classes with each containing one fifth of the total population |
5-4 | 4th quintile | The fourth of four values that divide the N measurementsinto a frequency distribution of five classes with each containing one fifth of the total population |