### Question:
SystematicSampling { public static double xbarStd(FlatDataCollection flatDataCollection) { return Math.sqrt(xbarVariance(flatDataCollection)); }  static FlatDataCollection randomSampling(FlatDataList idList, int n, boolean randomizeRecords); static double mean(FlatDataCollection flatDataCollection); static double xbarVariance(FlatDataCollection flatDataCollection); static double xbarStd(FlatDataCollection flatDataCollection);  }### Answer:
@Test public void testXbarStd() { logger.info("xbarStd"); FlatDataCollection flatDataCollection = generateFlatDataCollection(); double expResult = 20.143237078484; double result = SystematicSampling.xbarStd(flatDataCollection); assertEquals(expResult, result, Constants.DOUBLE_ACCURACY_HIGH); }