6. How to calculate Average Precision Things change at 3 hits Remember, the third item is not relevant, so we skip this one.
7.
8.
9. Average Precision Step 1 The Math: Summary Pretend the search stopped at #1 1 relevant hit/ 1 total hits = 1 Pretend the search stopped at #2 2 relevant hits/2 total hits = 1 Pretend the search stopped at #3 Not relevant –we skip this one Pretend the search stopped at #4 3 relevant hits/4 total hits=0.75 Pretend the search stopped at #5 4 relevant hits/5 total hits=0.8
If math makes your head explode, but you would like to understand how to calculate the precision, average precision and mean average precision of a database our search engine, this slidecast will help you. Anyone who has used a search engine like Google or a database of articles like EBSCOHost will have found that not all the retrieved articles are related to your search topic. There are always a few items that really don’t belong. Precision is a measurement of the effectiveness of the search engine to retrieve only those articles that are RELEVANT to your search.
![How to calculate precision ,[object Object],[object Object],[object Object],[object Object],[object Object],Relevant hits Total hits](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)