Using Excel to Find A Curve of Best Fit


Situation - The following data is from the lumber industry, giving the approxiate number of board feet of lumber per tree in a forest of a given age in years. What function will fit the data? Predict the harvest for ages other than those given.


Step 1 - The first thing I did was create a scatter plot of the data.


Step 2: Analysis of the Graph - The data is certainly not linear, I'm thinking it's quadratic.


Step 3: Trial and Error - Try various quadratic functions to see if they "match" your data.

a) First trial : y = .0075x²

Data Table:

Graph of data compared to original data:

b) Second Trial : y = .008x²

Data Table:

Analysis: I felt this was close, but still a little low for lumber harvest for values ranging from 80 to 120 yrs.

c) At this point I felt I was pretty spot on, so I used regression analysis that came up with the curve: y = .001x² - .68x + 13.3 with R² = .999 (YAY!)

Data Table:

Graph of data against original data:

Analysis: Looks Good! Spot On! Don't you just love Statistics :-)?

c) Completing the table and finding the missing values. Going to let y = .001x² - .68x + 13.3

Data Table with Predicted Values: