Some people think that an apronym is only a 'real' apronym if it has no extra, uncapitalised words, such as the 'in' in the expansion of HABIT: Have A Big Interest in Tobacco? In particular, Edwin Hermann requested on the forums that this site should only include apronyms without any such extra words. Tony McCoy O'Grady responded that 'real' acronyms have historically included (or even excluded) surplus words. As a compromise, there is now an option on all apronym list pages to only show 'perfect' apronyms -- that is, apronyms with no uncapitalised words in the expansions. By default, all apronyms are shown, but you can elect to show only 'perfect' apronyms by clicking 'Perfect Apronyms Only'.
You can see the full discussion at: http://www.co.nz/cgi/forums/list.cgi?id=acronyms&user=&session=&root=962748343.
If you view all apronyms, then beside each apronym in a list, you will see the apronym's 'purity' expressed as a percentage. This does not reflect anybody's opinion on the apronym, nor its suitability for showing to young children. It's simply a measure of how few 'extra' words are in the expansion, calculated automatically as the ratio of capitalised words to uncapitalised ones. For example, HABIT has a purity rating of 83%, because out of six words in the expansion, only five have their initials in the expansion. This gives a purity ratio of 5/6, or 83%. A 'perfect' apronym has a purity rating of 100%.