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When to use natural logs in log transformation?
I n log transformation you use natural logs of the values of the variable in your analyses, rather than the original raw values. Log transformation works for data where you can see that the residuals get bigger for bigger values of the dependent variable.
Which is the only variable that is log transformed?
Only the dependent/response variable is log-transformed. Exponentiate the coefficient, subtract one from this number, and multiply by 100. This gives the percent increase (or decrease) in the response for every one-unit increase in the independent variable.
How to convert the mean of a log transformation to raw units?
Convert the mean of the log-transformed variable back to raw units using the back-transformation Y = e mean (if your transformation was Z = logY) or Y = e mean/100 (if you used Z = 100logY). Keep the standard deviation as a percent variation or coefficient of variation (CV).
How to interpret log transformations in a linear model?
OK, you ran a regression/fit a linear model and some of your variables are log-transformed. Only the dependent/response variable is log-transformed. Exponentiate the coefficient, subtract one from this number, and multiply by 100. This gives the percent increase (or decrease) in the response for every one-unit increase in the independent variable.
What does it mean to have zero values in log transformation?
Having (a considerable amount of) zero values indicates that there might be a problem, either with data generation (truncation, rounding errors, sensitivity limit,…) or that the data generating process might not be multiplicative. This could be a warn signal not to simply log-transform the data.
How to calculate the CV of a log transformation?
Calculate this CV in the same way as for differences or changes in the variable: if SD is the standard deviation of the log-transformed variable, the approximate CV is simply 100SD, and the exact CV is 100 (e SD – 1). If you used 100log for your transformation, the approximate CV is simply the SD itself, and the exact CV is 100 (e SD/100 – 1).
When to use log transformed variable in statistics?
In such situations, the analysis of the log-transformed variable provides the most accurate estimate of the percent change or difference. Make sure you use natural logs, not base-10 logs, then analyze the log-transformed variable in the usual way. Suppose you end up with a difference of 0.037 (you’ll often get small numbers like this).