It does at ;least provide a middle ground, where the final figure may be less or greater than that. It gives an average based on a sample group. I was surpised by the difference between the typical/average vs perfect numbers especially with nuvaring (which ive had experience with before). It’s a higher number than I would have expected for the various methods, so thanks @Parsifal for posting the graphic. It gives a bit of a sense of what is possible for a random sample group.
For the record, I enjoyed condom free with a regular partner for many years with nuvaring and over many hundreds of experiences, probably no more than one incident where a secondary method was used. That it could have only been 92% is an interesting stat to know.
Perhaps skepticism on effectiveness is a good general rule