Refactor variance

src/stats/compute.js

@@ -4,7 +4,7 @@ import { getLengthFromLoops } from './length.js'
 import { getMoe, getRmoe } from './moe.js'
 import { getOutliersPercentages } from './outliers/main.js'
 import { getSortedMedian, getQuantiles } from './quantile.js'
-import { getStdev, getRstdev } from './stdev.js'
+import { getVariance, getStdev, getRstdev } from './stdev.js'
 import { getMean } from './sum.js'
 
 // Aggregate measures into discrete statistics.
@@ -121,7 +121,8 @@ const getPrecisionStats = function ({
     return getPerfectPrecisionStats(mean)
   }
 
-  const stdev = getStdev(measures, { minIndex, maxIndex, mean })
+  const variance = getVariance(measures, { minIndex, maxIndex, mean })
+  const stdev = getStdev(variance)
   const rstdev = getRstdev(stdev, mean)
   const moe = getMoe(stdev, length)
   const rmoe = getRmoe(moe, mean)

src/stats/stdev.js

@@ -1,18 +1,13 @@
-// Retrieve standard deviation of an array of floats (cannot be NaN/Infinity).
+// Retrieve variance of an array of floats (cannot be NaN/Infinity).
 // Array must not be empty.
-// We use the absolute standard deviation, as opposed to making it relative to
-// the mean (as a percentage)
+// We use the absolute variance, as opposed to making it relative to the mean
+// (as a percentage)
 //  - It makes it easier to understand:
 //     - the spread of a given combination
 //     - its relation to moe and distribution-related stats such as percentiles
 //       (that are also not percentages)
 //  - On the flipside, it makes it harder to compare combinations (since they
 //    most likely have different means)
-export const getStdev = function (array, { minIndex, maxIndex, mean }) {
-  const variance = getVariance(array, { minIndex, maxIndex, mean })
-  return Math.sqrt(variance)
-}
-
 export const getVariance = function (
   array,
   { minIndex = 0, maxIndex = array.length - 1, mean },
@@ -35,6 +30,11 @@ const getSumDeviation = function ({ array, minIndex, maxIndex, mean }) {
   return sum
 }
 
+// Retrieve standard deviation
+export const getStdev = function (variance) {
+  return Math.sqrt(variance)
+}
+
 // Retrieve stdev relative to the mean.
 // This is more useful than stdev when comparing different combinations, or when
 // targetting a specific precision threshold.