| import 'dart:math' as math; |
| |
| class SimpleTTestStat { |
| static TTestResult ttest(List<int> a, List<int> b) { |
| int aSum = a.reduce((value, element) => (value + element)); |
| int bSum = b.reduce((value, element) => (value + element)); |
| int aCount = a.length; |
| int bCount = b.length; |
| double aMean = aSum / aCount; |
| double bMean = bSum / bCount; |
| double aVariance = variance(a); |
| double bVariance = variance(b); |
| double pooledStandardDeviation = math.sqrt((aVariance + bVariance) / 2); |
| double pooledSampleStandardError = |
| pooledStandardDeviation * math.sqrt(1 / aCount + 1 / bCount); |
| double diffMean = aMean - bMean; |
| |
| // Difference in population mean with confidence interval: |
| // μ1 - μ2 = (M1 - M2) ± t * standardError |
| double confidence = |
| tTableTwoTails_0_05(aCount + bCount - 2) * pooledSampleStandardError; |
| |
| if (confidence < diffMean.abs()) { |
| double percentDiff = diffMean * 100 / bMean; |
| double percentDiffConfidence = confidence * 100 / bMean; |
| return new TTestResult( |
| true, percentDiff, percentDiffConfidence, diffMean, confidence); |
| } else { |
| return new TTestResult(false, 0, 0, 0, 0); |
| } |
| } |
| |
| static double variance(List<int> data) { |
| int sum = data.reduce((value, element) => (value + element)); |
| int count = data.length; |
| double average = sum / count; |
| |
| double diffSquareSum = 0; |
| for (int value in data) { |
| double diff = value - average; |
| double squared = diff * diff; |
| diffSquareSum += squared; |
| } |
| |
| double variance = diffSquareSum / (count - 1); |
| return variance; |
| } |
| |
| static double tTableTwoTails_0_05(int value) { |
| // TODO: Maybe actually calculate this? I haven't looked that up. |
| // These numbers are from google sheets "=TINV(0.05, value)" |
| if (value < 1) throw "value has to be > 0"; |
| if (value == 1) return 12.70620474; |
| if (value == 2) return 4.30265273; |
| if (value == 3) return 3.182446305; |
| if (value == 4) return 2.776445105; |
| if (value == 5) return 2.570581836; |
| if (value == 6) return 2.446911851; |
| if (value == 7) return 2.364624252; |
| if (value == 8) return 2.306004135; |
| if (value == 9) return 2.262157163; |
| if (value == 10) return 2.228138852; |
| if (value == 11) return 2.20098516; |
| if (value == 12) return 2.17881283; |
| if (value == 13) return 2.160368656; |
| if (value == 14) return 2.144786688; |
| if (value == 15) return 2.131449546; |
| if (value == 16) return 2.119905299; |
| if (value == 17) return 2.109815578; |
| if (value == 18) return 2.10092204; |
| if (value == 19) return 2.093024054; |
| if (value == 20) return 2.085963447; |
| if (value <= 30) return 2.042272456; |
| if (value <= 40) return 2.02107539; |
| if (value <= 50) return 2.008559112; |
| if (value <= 60) return 2.000297822; |
| if (value <= 70) return 1.994437112; |
| if (value <= 80) return 1.990063421; |
| if (value <= 80) return 1.990063421; |
| if (value <= 90) return 1.986674541; |
| if (value <= 100) return 1.983971519; |
| if (value <= 150) return 1.975905331; |
| if (value <= 200) return 1.971896224; |
| if (value <= 250) return 1.969498393; |
| if (value <= 500) return 1.964719837; |
| if (value <= 1000) return 1.962339081; |
| if (value <= 10000) return 1.96020124; |
| if (value <= 100000) return 1.959987708; |
| if (value <= 1000000) return 1.959966357; |
| return 1.959964228; |
| } |
| } |
| |
| class TTestResult { |
| final bool significant; |
| final double percentDiff; |
| final double percentDiffConfidence; |
| final double diff; |
| final double confidence; |
| |
| TTestResult(this.significant, this.percentDiff, this.percentDiffConfidence, |
| this.diff, this.confidence); |
| |
| String toString() { |
| if (significant) { |
| double leastConfidentChange; |
| if (diff < 0) { |
| leastConfidentChange = diff + confidence; |
| } else { |
| leastConfidentChange = diff - confidence; |
| } |
| return "TTestResult[significant: " |
| "${_format(percentDiff)}% +/- ${_format(percentDiffConfidence)}% " |
| "(${_format(diff)} +/- ${_format(confidence)}) " |
| "(at least ${_format(leastConfidentChange)})]"; |
| } else { |
| return "TTestResult[not significant]"; |
| } |
| } |
| |
| String _format(double d) { |
| return d.toStringAsFixed(2); |
| } |
| } |