correlation coefficient problem

Asked Dec 12 '13 at 15:24

Active Dec 12 '13 at 15:26

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The national farming association has data on the amount of pesticide used per acre and the percentage of fruit that has been contaminated by insects per acre, for $117$ farms. These two variables have a correlation coefficient $r=-0.8$. For a farm that uses an amount of pesticide that is $2$ standard deviation above the mean amount of pesticide used, we would predict the percentage of contaminated fruit will be $1.6$ SD below the mean.

Can anyone explain how $1.6$ below the mean is calcuated to me? I can only think of sum of $\cfrac{z_x z_y}{n-1}= r.$

edited Dec 12 '13 at 15:26

quapka

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asked Dec 12 '13 at 15:24

natsu

$-1.6=2 \times (-0.8)$. – hhsaffar Dec 12 '13 at 15:30
what formula is that? – natsu Dec 12 '13 at 15:31
First, this is not an exact formula, this is a prediction. There is usually some error. You may find this helpful http://onlinestatbook.com/2/regression/intro.html – hhsaffar Dec 12 '13 at 15:37

correlation coefficient problem

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