98% (or 95, 99, etc) effective

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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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5 Answers

Anonymous 0 Comments

Very few things in biology are 100% consistent, so when it comes to effectiveness, manufacturers account for outliers…the especially resistant bugs…in their effectiveness claims. From statistics, we would expect an outlier to be in the range of 1.5-3% (up to 5%, depending on who you talk to).

If manufacturers claimed 100% effectiveness, they’d be getting sued every time someone could prove they used the product as directed and still got sick.

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