Versus Last ... - what do you do?

[gingerafro]

I'm having a debate regarding the presentation of some percentage increases / decreases.
Lets say that last year we made £500k profit and this year £620k, the VLY is

(620/500-1)x100 = +24%

However, what if one of the numbers is negative?

Then we get:

(-620/500-1)x100 = -224%
or
(620/-500-1)x100 = -224%

How would you present this?
I have added a poll to add to this discussion - which has probably been held on another thread before.

 

[nbrcrunch]

We could argue this all day but it really depends on the business and the administration. I've had instances where I was reporting variance and the administration wanted to see the percentage of variance. They didn't care whether it was positive or negative, "Just give us the percentage." The resulting formula incorporated ABS() (absolute value) to strip out the negative signs.

Lesson learned: "Right" is not defined by technical or mathematical correctness. It is defined by business drivers and what "the boss" expects to see.

 

[schielrn]

You really have lost 224% of profits compared to the previous year. One year you made 500 and then the next you lost 620 which yould be a swing of 1,120. So saying it was only a -24% decrease or -124% decrease would be wrong in my opinion?

 

[Andrew Fergus]

I'm having a debate regarding the presentation of some percentage increases / decreases.
Lets say that last year we made £500k profit and this year £620k, the VLY is

(620/500-1)x100 = +24%

However, what if one of the numbers is negative?

Then we get:

(-620/500-1)x100 = -224%
or
(620/-500-1)x100 = -224%

How would you present this?
I have added a poll to add to this discussion - which has probably been held on another thread before.

I would show -620/500 as -224%
but
I would show 620/-520 as +224%
given a + is a 'positive' symbol and there is improved result vs last year.

The other interesting one is if you end up with a divisor of 0 - do you show +/- 100% or 0%? I opt for the +/- 100% despite the fact it is technically infinite.

So long as your readers understand the convention used then it shouldn't be an issue.

Andrew