G only) Why is the value of the covariance “incorrect” on the HP38G?
Question submitted by: Chris Williams; Bunbury Cathedral Grammar School Answer: The value is not actually incorrect at all. The values of the variance, standard deviation and covariance all have two possible values depending on whether you want the population or sample values. The population value is obtained by dividing by n and is used when the data you are using in your calculation is the entire population. The sample value comes from dividing by n-1 rather than n, and is used when the data you are using in your calculation is small in comparison to the population from which it is drawn. In this case you are wanting to use the sample to estimate what the values from the entire population would be. At high school level we only use the population values rather than the sample values. The sample versions may only become important at university level where you might be doing research in which you were generalizing to the whole population from a limited sample. In the case of the HP38G,
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