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pol 51 lecture 12

# pol 51 lecture 12 - B uggey whip used on animals So when...

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Buggey whip used on animals. So when people say “buggey whip” they mean obsolete technology. Whenever you’re working with data, just use pictures. Measuring fit, use R-squared statistic, which ranges between zero and one -> indicates the proportion of the variation in Y (dependent variable) that is accounted for by the model. Total variation, use TOTAL SUM OF SQUARES. Residual variation in Y, use RESIDUAL SUM OF SQUARES. Big residuals are bad because residuals are leftovers, the unexplained. Now that we have TSS and RSS, we can calculate R 2 . We can also use MODEL SUM OF SQUARES (MSS) in place of RSS when calculating R 2 . MSS + RSS = TSS Explained + Unexplained = All This gives a number between 0 and 1, where 1 is really good. So, for example, .55 means that 55% of variance of Y is explained by X. B is a slope, summarizes what we know. We also have some idea of how close B is to Bhat. The standard deviation of the parameter is called the STANDARD ERROR, which comes

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