Difference between p, percent and ppm

In the Quality world, practitioners may choose to measure quality on different scales. Some may use the p or the proportion metric, others may choose percent or ppm calculation.

What is the difference between p, percent or ppm metric?

There is a fundamental difference between the proportion, percentage, ppm calculations. And that is the base each of these calculations use. The proportion calculation uses a base of 1, percent uses a base of 100 and ppm uses a base of million.

For example, if I had to find proportion, percent and ppm for 5 defective parts found in a lot of 300..
proportion defective = 5/300 = 0.0167
percent defective = (5/300) x 100 = 1.67%
defective ppm = (5/300) x 1000000 = 16666.67ppm

The ratio is the same 5/30, but the multiplier changes when calculating proportion, percent or ppm values for defectives found in a lot.

What metric do you use for measuring quality of your product/service?
Which metric is better - p, percent or ppm?
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