When something is 98% effective, what does that mean?
For example, a cleaning product that says it’s 98% effective at removing germs from surfaces.
* Does it clean 98% of all germs away and leave 2% behind?
* Of all known germs, are 2% of them totally immune to this cleaner, so it can only hope to clean the other 98%?
* Is it that out of 100 people, 98 will be able to clean the surface to 100% clean and the other 2 won’t?
* Does the product work on 98% of surfaces, but there are some surfaces, say the metal bolts on a toilet, that the product just can’t clean?
* Is the product actually 100% effective, but in tests 2% of people drank it instead of wiped the counter with it?
How can you really tell what an effectiveness rating is measuring?
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This is less about mathematics and more about just pure language.
How come 10% more of 100 is 110 but 10% less of 110 is 99?
It’s just because percentages are relative to a quantity. The word “effective” doesn’t explicitly reveal the product’s intent. Given the body of your question, it’s usually used to say 98% of germs don’t survive application of the cleaning agent, but I can’t promise you that’s always the case. Percentages are dimensionless (unlike say 30 mph) so you can assign it anything you want.
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