I got stuck to find a fair formula to calculate the average ranking of the items that I found after consecutive searches, look:
If I calculate the simple average of the item2 for example I get 1,33 as a result, not even nearly close to an "average" ranking :P
any ideas?
What are the values in the table? Are they rankings under the three searches? Then you can just average (or sum-gets the same thing and removes the division) the numbers, rank them, and report the result. $1.33333$ for item $2$ is not bad, actually. It will probably be worst (if low numbers are bad), which is exactly what you want-it was very low by all three rankings. You would still have to deal with items that are not ranked by all three searches. Ties in one search are no problem, and you may have ties in the final ranking in this approach.