feat(benchmark): add statistical functions to calculate confidence in…

…terval

benchmark/web/bp.js

@@ -1,4 +1,8 @@
 var bp = window.bp = {};
+bp.Statistics = {
+  //Taken from z-table where confidence is 95%
+  criticalValue: 1.96
+};
 bp.steps = window.benchmarkSteps = [];
 bp.runState = {
   numSamples: 20,
@@ -9,6 +13,36 @@ bp.runState = {
   timesPerAction: {}
 };
 
+bp.Statistics.getConfidenceRange = function(mean, confidenceInterval) {
+  return [
+    mean - confidenceInterval,
+    mean + confidenceInterval
+  ];
+};
+
+bp.Statistics.calculateConfidenceInterval = function(standardDeviation, sampleSize) {
+  var standardError = standardDeviation / Math.sqrt(sampleSize);
+  var marginOfError = bp.Statistics.criticalValue * standardError;
+  marginOfError = Math.round(marginOfError * 100) / 100;
+  return marginOfError;
+};
+
+bp.Statistics.calculateStandardDeviation = function(sample) {
+  var mean = 0;
+  var deviation = 0;
+  sample.forEach(function(x) {
+    mean += x;
+  });
+  mean = mean / sample.length;
+
+  sample.forEach(function(x) {
+    deviation += Math.pow(x - mean, 2);
+  });
+  deviation = deviation / sample.length;
+  deviation = Math.sqrt(deviation);
+  return deviation;
+};
+
 bp.setIterations = function (iterations) {
   bp.runState.iterations = iterations;
 };

benchmark/web/bp.spec.js

@@ -34,6 +34,30 @@ describe('bp', function() {
     };
   });
 
+  describe('.Statistics', function() {
+    describe('.calculateConfidenceInterval()', function() {
+      it('should provide the correct confidence interval', function() {
+        expect(bp.Statistics.calculateConfidenceInterval(30, 1000)).toBe(1.86);
+      });
+    });
+
+
+    describe('.calculateStandardDeviation()', function() {
+      it('should provide the correct standardDeviation for the provided sample', function() {
+        expect(bp.Statistics.calculateStandardDeviation([
+          2,4,4,4,5,5,7,9
+        ])).toBe(2);
+      });
+    });
+
+
+    describe('.getConfidenceRange()', function() {
+      it('should return an array of low and high confidence range', function() {
+        expect(bp.Statistics.getConfidenceRange(100, 1.5)).toEqual([98.5,101.5]);
+      });
+    });
+  });
+
   describe('.loopBenchmark()', function() {
     var runAllTestsSpy, btn;
     beforeEach(function() {