The text book says the residual diagram suggests that the variances of the error terms are equal.But how the variances of the error equal?As You can see the variance on the right circle is greater than the left one
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The textbook describes the ideal scenario. Your analysis has probably a few assumptions. Checking whether the variance of the residual is equal, is a way to check whether some of them are met or violated. If they are equal, you're fine, if not, technically your analysis is not valid. Just from looking on your plot, I'd say that the variances are equal enough for the analysis to be acceptable, but in the end it is your decision. In general, the variances don't have to be exactly the same, as long as there is no large deviation and no systematic trend, you should be good.
btw. it would be a wise move, to give a bit more detail on the textbook, your problem, the analysis. The more detail you give, the better people can answer you.
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