Refactoring

ehmicky · Dec 19, 2021 · 4a2012d · 4a2012d
1 parent bc7b87c
commit 4a2012d
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Showing 3 changed files with 16 additions and 7 deletions.
diff --git a/src/stats/critical_values/student_t.js b/src/stats/critical_values/student_t.js
@@ -3,17 +3,15 @@ import { getCriticalValue, getCriticalValuesMap } from './map.js'
 
 // Retrieve critical value of the Student's t distribution, two-tailed, for a
 // given degrees of freedom
-export const getStudentTValue = function (degreesOfFreedom) {
-  const singleSignificanteLevel = (1 - SIGNIFICANCE_LEVEL) / 2
+export const getStudentTValue = function (degreesOfFreedom, significanceLevel) {
+  const singleSignificanteLevel = (1 - significanceLevel) / 2
   return getCriticalValue(
     STUDENT_T_MAP,
     degreesOfFreedom,
     singleSignificanteLevel,
   )
 }
 
-const SIGNIFICANCE_LEVEL = 0.95
-
 const STUDENT_T_RAW = [
   {
     significanceLevel: 0.025,

diff --git a/src/stats/moe.js b/src/stats/moe.js
@@ -76,7 +76,7 @@ export const getAdjustedMoe = function (stdev, length, envDev) {
 //    combination pair
 export const getMoe = function (stdev, length) {
   const standardError = stdev / Math.sqrt(length)
-  const tvalue = getStudentTValue(length - 1)
+  const tvalue = getStudentTValue(length - 1, SIGNIFICANCE_LEVEL)
   const moe = standardError * tvalue
   return moe
 }
@@ -122,7 +122,11 @@ export const getLengthForMoe = function (moeTarget, stdev) {
     lengths.add(length)
     // eslint-disable-next-line fp/no-mutation
     length = Math.max(
-      Math.round(((getStudentTValue(length - 1) * stdev) / moeTarget) ** 2),
+      Math.round(
+        ((getStudentTValue(length - 1, SIGNIFICANCE_LEVEL) * stdev) /
+          moeTarget) **
+          2,
+      ),
       MIN_LENGTH,
     )
   }
@@ -132,3 +136,5 @@ export const getLengthForMoe = function (moeTarget, stdev) {
 
 // Minimal `length` with a defined t-value
 const MIN_LENGTH = 2
+
+const SIGNIFICANCE_LEVEL = 0.95
diff --git a/src/stats/similar.js b/src/stats/similar.js
@@ -123,10 +123,15 @@ const welchTTest = function ({
   const degreesOfFreedom =
     (errorSquaredA + errorSquaredB) ** 2 /
     (errorSquaredA ** 2 / (lengthA - 1) + errorSquaredB ** 2 / (lengthB - 1))
-  const tValue = getStudentTValue(Math.floor(degreesOfFreedom))
+  const tValue = getStudentTValue(
+    Math.floor(degreesOfFreedom),
+    SIGNIFICANCE_LEVEL,
+  )
   return tStat < tValue
 }
 
 const getErrorSquared = function (stdev, length) {
   return (stdev / Math.sqrt(length)) ** 2
 }
+
+const SIGNIFICANCE_LEVEL = 0.95