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Bernard Cleyet, offered an interesting question to my comment on log-log plots.
RB: "If I want my students to do a log-log plot, I actually prefer to have them make two extra columns of their data (log(x) and log(y)) and then plot these new columns as an xy scatter plot. To this data they can then add a linear trendline in Excel."
BC: "Am I unnecessarily suspicious that the error(s) (Chi-Square, etc.) will differ?
"Heuristically, I prefer the students to do both methods, i.e. plot linear and fit, plot log and fit, either, or both, plot log of data on lin. graph and plot original data on log paper."
RB (Now): I know this is a complicated problem, and I don't have time to pursue it now. However, my sense is that when we "eye-ball" a good straight-line to the data on a log-log plot, we are in fact doing an imprecise least-squares fit to the log-log data and not to the raw data. With the very high R-squared values (and what does that mean for log-log plots?) that we usually work with in undergraduate labs, probably none of these concerns make a large difference in the constants of the defining relationship.
Richard Bowman
Bridgewater College
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