which value of n to use in a regression line when a value is transformed

[Bryn]

In 1980 a river was restocked with fish. The local angling club kept a record of the number of fish, y caught on a stretch of the river t years after restocking. Some of the records are given in the table below.

 

t    1   2   3   4   5   7  10  12
y   185 170 172 166 164 159 162 157

 

The regression line y on x is y=177.28 -1.89t

 

An alternative model is produced using the new variable x=1/t which gives the following

 

SUM(x) = 2.6095

SUM(x^2) = 1.5010

SUM(y) = 1335

SUM(xy) = 453.6310

 

Caluculate the regression equation of y on x in the form y = a+bx

 

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I got the equation y = 73+175x when using n=12 (as the max of t is 12) but the answer is y = 158 + 28x.

 

What value of n do i use for caluclulating Sxx and Sxy?

[bloodhound]

no, thats wrong.

 

the value of n in [math]s_{xy}[/math] and [math]s_{xx}[/math] is the total number of pairs of observations. ie.[math](x_i,y_i)[/math]

[Bryn]

so n=8?

[Dave]

Yeah, the value of n doesn't change.