Forecast, Growth Functions

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Hello all,

In my worksheet I have column A (Sales Volume) and column B(Labor Hours Allowed). When charted, the data resembles a logarithmic curve. I have tested the Forecast and Growth functions on a 5 point sample, but I get a straight line and an exponential curve when charted (which is exactly what MS says they do).

Is there another function or method that might accurately forecast or project the data based on a small sample in such a way that the projected data resemble a logarithmic curve when charted?

I have attached a small workbook with one sheet…

Thanks,
Michael Read

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Michael,

Did you try the Excel built-in trendlines? Therefore, you first need to plot your data in a XY-scatter plot. Then, select the datapoints in your chart and click the right-button of the mouse to obtain a popup menu. Choose Add Trendline, and you will be able to try out different mathematical functions, including the exponential and logarithmic functions. Choosing the Options tab allows you to display the equation and to forecast outside the range of your datapoints.
Don’t know if this is of any help?

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Hi Hans,

Shortly after I made the first post, I “discovered” the trendline option to display the formula. I have been playing around with it, but generally when I plug my number in, say for “x”, I get some outrageous number like 3,289,345 for the y (the labor hours on my attachment). I am going to play with it some more, I might possibly be coding the formula wrong or have the “x” wrong. It’s been a while since I took statistics in college! Thanks for your help.

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Hi Mike,

You have probably seen on my profile that I am a statistician. I sometimes give statistics courses to my colleagues and I always state that Extrapolation (or forecasting) is a very dangerous thing to do. Just read the words of Mark Twain:

“In the space of one hundred and seventy-six years, the Lower Mississippi has shortened itself two hundred and forty-two miles. This is an average of a trifle over one mile and an third per year. Therefore, any calm person, who is not blind or idiotic, can see that in the Old O

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Thanks Hans, point well made…

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