Hallo,
by definition the regression line should go through the conditional means of Y-variable in each X-variable. But when I compute conditional means of Y in each category of X the regression line does not go through these conditional means.
In statistical literature concerning regression I have found this explanation: we work with sample and therefore we do not have all observations of Y variable in each X-variable, and this is the reason why we do not observe the correspondence among measured conditional means of Y variable and predicted conditional means given by regression line.
Is this explanation correct and just one possible?
Thanks. Tomas
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