Every couple of months, I get asked by management at work to produce a statistical report of what’s been going on in our team. How many times X occurred, how many times we had to Y etc.
It’s the least favourite part of my job.
The least favourite part of the least favourite part of my job is working out percentages, and percentage difference; mostly because I can never remember the formulae involved and thus much frantic Googling ensues. For future reference, here they are:
Percentages:
A percentage is a fraction, multiplied by one hundred. 1/2, or “one in two”, multiplied by one hundred gives us fifty; or “fifty percent”. 2/8, or “two parts in eight” multiplied by one hundred gives us twenty five; or “twenty five percent”.
If you have ten horses, and eight of the ten (”8/10″) are palominos, then:
8/10 * 100 =
80
…eighty percent are palominos.
Percentage Difference:
Sometimes you want to know how much a thing has increased, or decreased over time. The formula for this is (difference/original total) times one hundred. Say we get another shipment of horses; this time six out of the ten are palominos. The “difference” is two (six minus eight); and the “original total” is the eight palominos we had in the first batch. So:
((6-8)/8) * 100 =
(-2/8) * 100 = -25
…or this shipment is 25% lower in palominos than the last.
As an exercise for the reader, figure out the percentage of fat in full cream (nine grams per 250ml) and skim milk (0.25 grams per 250 ml); and the percentage difference between them.
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