# Determining Line of best fit

• Nov 21st 2009, 02:17 PM
lexx
Determining Line of best fit
I have to figure out the line of best fit for children's books, the following data is given.
Recommended Age Leve - Mean Word Length
4 - 3.5
6 - 5.5
5 - 4.6
6 - 5.0
7 - 5.2
9 - 6.5
8 - 6.1
5 - 4.9
So i went ahead and made a table for x, y, x*y, x2 and y2 then i imputed the following data. Does this look anywhere close to being right?

Slope = n(Sigma(xy)) - (Sigma(x)) / n(Sigma(x2)) - (Sigma(x))2
= 8(268.2) - (50)(41.3) / 8(332) - (50)2
= 2145.6 - 2065 / 2656 - 2500
= 80.6 / 156
= 0.52

Intercept = Sigma(y) - m(Sigma(x)) / n
= 41.3 - 0.52(50) / 8
= 1.9125

y = mx + b
y = 0.52x + 1.91

then looking at this if i go to figure out what the average word length is for a 12 year-old i get 4.33... that's even less then what's recommended for a 6 year old?!?!?! Is there somewhere in here where i'm going wrong?
• Nov 21st 2009, 09:14 PM
Robb
checked using eviews and the model is correct.

For a 12 year old, i got 8.15=12*.52+1.91