In the docs (file:///C:/Libraries/boost/boost_1_39_0/doc/html/accumulators/user_s_guide.htm l#accumulators.user_s_guide.the_statistical_accumulators_library.variance) there is an example of calculating variance of values 1,2,3,4,5 accumulator_set<int, stats<tag::variance(lazy)> > acc1; acc1(1); acc1(2); acc1(3); acc1(4); acc1(5); BOOST_CHECK_EQUAL(5u, count(acc1)); BOOST_CHECK_CLOSE(3., mean(acc1), 1e-5); BOOST_CHECK_CLOSE(11., moment<2>(acc1), 1e-5); BOOST_CHECK_CLOSE(2., variance(acc1), 1e-5); When I am doing the same in Excel the mean is indeed 3, which matches the example, but variance is 2.5 and not 2. I am using AVERAGE and VAR formulas in Excel for mean and variance respectively Why there is a mismatch between variance values??