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Example o saumples frae twa populations wi the same mean but different variances. The reid population haes mean 100 an variance 100 (SD=10) while the blue population haes mean 100 an variance 2500 (SD=50).

In probability theory an stateestics, variance is the expectation o the squared deviation o a random variable frae its mean. Informally, it meisurs hou faur a set o (random) nummers are spreid oot frae thair average vailyie. Variance haes a central role in stateestics, whaur some ideas that uise it include descriptive stateestics, stateestical inference, hypothesis testin, guidness o fit, an Monte Carlo saumplin.