### Question:
BasicRiskDifference extends AbstractBasicRelativeEffect<RateMeasurement> implements BasicRateRelativeEffect { @Override public Double getError() { if (!isDefined()) return Double.NaN; double a = getA(); double b = getB(); double n1 = a + b; double c = getC(); double d = getD(); double n2 = c + d; return new Double(Math.sqrt(a*b/Math.pow(n1,3) + c*d/Math.pow(n2,3))); } BasicRiskDifference(RateMeasurement baseline, RateMeasurement subject); @Override Double getError(); @Override boolean isDefined(); String getName(); Distribution getDistribution(); RelativeEffect<RateMeasurement> getCorrected(); @Override AxisType getAxisType();  }### Answer:
@Test public void testGetErrorvsCooper() { assertEquals(s_cooper1977RDvar,square(d_cooperRD.getError()),0.001); }