Who is asking: Other
Level: All
Name: Remo

Question:
In the year 2000 300 out of a possible 600 completed a phone survey for a total of 50% completion rate.
In the year 2001 20 out of 100 possible people completed the survey when it was re-done. This is a completion rate of 20%
To figure out the percentage change between the years can just use the difference between the percentage figures I already have? Or can I calculate it the same as you would for non-percentage numbers. For example you gave an example here of a salary increase from $20 to $95 being an increase of 375%.
Would I solve my problem the same way expect substituting my percentages (.5 and .2) in place of $20 and $95?

Hi Remo,

When you report something as a percentage you should ask yourself "percentage of what?" The 50% completion rate in 200 is 50% of 600. The 20% completion rate in 2001 is 20% of 100. If you simply subtract the two percentages to get -30% then it's -30% of what? This difference doesn't make any sense.

You say that you want the percentage change. The completion rate started at 0.5 and changed to 0.2 so what you need is to express this change as a percentage of where it started. That is you want 0.2 - 0.5 = -0.3 as a percentage of 0.5.

 ^0.2-0.5/_0.5 = -0.6

and thus the completion rate decreased by 60% from 2000 to 2001.

Cheers,
Penny

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