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AP Stats Help - Imagine - 2010-10-20
I have the following data:
x l y
0.5 33.3
1.0 58.3
1.5 81.8
2.0 96.7
2.5 100.0
I am told to either use the square root of x or log(x) instead of x. I use the square root of x as my transformation, replace it with x, and find the equation of the original equation using a linear reg on the transformed data. Here's the problem: When I plug 1.75 into my calculated linreg equation, I get ~23.3, which is wayyy offf of the actual value (I put the equation in the form of y=a+b(rootx). Did I do something wrong, or did I just use the wrong transformation?
AP Stats Help - Russt - 2010-10-20
So... transform the list:
| root(x) | y |
| 0.707 | 33.3 |
| 1 | 58.3 |
| 1.225 | 81.8 |
| 1.414 | 96.7 |
| 1.581 | 100.0 |
LinReg -> I get y = -21.505 + 80.582root(x). Residual plot is questionable at best, but disregarding that for now...
-21.505 + 80.582root(1.75) = 85.095, which seems reasonable. Not sure what you did wrong.
AP Stats Help - Imagine - 2010-10-20
Looking at what you got, I think I might have accidentally linreg'd the original data.