Monthly Archives: September, 2013

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A tool which is often left aside : the class person The class person is useful to keep information like name and email address about one person or a group of. Some problem arose to me when I tried to convert an object of this class to a well-specified data frame. So, I implemented a …

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A practical demonstration of linearity of MAD We know that if we have a variable named X, to which we apply a linear transformation like Y = a X + b we can demonstrate that the computation of indexes related to Y may be easily deduced from the indexes we have obtained for X. This …

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Find a sample size for a T test When we want to test if a sample mean is significantly different from a certain known population’s mean, we usually use a T test with the following statistic: Tn = (sample.mean – mean) / (sample.sd / sqrt(n)) which has to be compared with a critical value of …

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