[R] OT: computing percentage changes with negative and zero values?
jim at bitwrit.com.au
Wed Feb 17 12:13:42 CET 2010
On 02/17/2010 04:06 AM, Liviu Andronic wrote:
> Dear all
> I need to compute percentage changes of my data, but unfortunately
> they contain both negative and zero values, and I am quite confused on
> how to proceed. Searching the internet I found that many people ran
> into similar issues, with no obvious solution available.
> As you have noticed, I'm quite unsure on how to proceed. My actual
> data represents financial EPS (earnings per share) forecasts, ranging
> from -1 to 5. So, it has a "natural zero point" (see David Winsemius'
> comments in ). However, I need to compute percentage variations
> since I am primarily interested in the evolution of the forecasts (for
> a given company), while EPS data between two companies are not
> necessarily comparable. The percentage data would subsequently be used
> in performing statistical analyses (regression, etc.).
My understanding of percentage change is the absolute value of the
change divided by the absolute value of the initial value and the result
multiplied by 100. Thus:
 283.720930 187.341772 10.144928 100.000000 Inf 52.980132
 212.676056 46.250000 35.042735 6.329114 223.648649 51.912568
 263.636364 150.000000 69.444444 959.090909 167.195767 40.157480
gives me correct values (and the Inf for the fifth value is correct, as
the denominator is zero). My definition might not be the only one, though.
More information about the R-help