### Question:
StratifiedSampling { public static double std(TransposeDataCollection sampleDataCollection, AssociativeArray populationNh) { return Math.sqrt(variance(sampleDataCollection, populationNh)); }  static TransposeDataCollection weightedProbabilitySampling(AssociativeArray2D strataFrequencyTable, AssociativeArray nh, boolean withReplacement); static TransposeDataCollection randomSampling(TransposeDataList strataIdList, AssociativeArray nh, boolean withReplacement); static double mean(TransposeDataCollection sampleDataCollection, AssociativeArray populationNh); static double variance(TransposeDataCollection sampleDataCollection, AssociativeArray populationNh); static double std(TransposeDataCollection sampleDataCollection, AssociativeArray populationNh); static double xbarVariance(TransposeDataCollection sampleDataCollection, AssociativeArray nh, AssociativeArray populationNh); static double xbarStd(TransposeDataCollection sampleDataCollection, AssociativeArray nh, AssociativeArray populationNh); static AssociativeArray optimumSampleSize(int n, AssociativeArray populationNh, AssociativeArray populationStdh);  }### Answer:
@Test public void testStd() { logger.info("std"); TransposeDataCollection sampleDataCollection = generateSampleDataCollection(); AssociativeArray populationNh = generatePopulationNh(); double expResult = 3.0722255132211; double result = StratifiedSampling.std(sampleDataCollection, populationNh); assertEquals(expResult, result, Constants.DOUBLE_ACCURACY_HIGH); }