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I got stuck to find a fair formula to calculate the average ranking of the items that I found after consecutive searches, look:

enter image description here

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?

kjetil b halvorsen
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deniswsrosa
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2 Answers2

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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.

Ross Millikan
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  • The numbers in the table are the ranking positions of the itens in each search, in that case low numbers are good. – deniswsrosa Apr 29 '14 at 14:08
  • Bbut zero is a "no result found" mark. So in a simple average, a zero result bring the number down, the exact oposite of what o would like. – deniswsrosa Apr 29 '14 at 14:15
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    And if I assign the worst value (100) to a "no result found", the average become a little "strange" (2+2+100)/3 = 34,67 – deniswsrosa Apr 29 '14 at 14:20
  • No result found is often problematic for things like this. You should probably just average the ones you have, so you will get $(2+2)/2=2$ – Ross Millikan Apr 29 '14 at 15:46
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The arithmetic mean is a parametric descriptive statistic that presumes normality in the data. Ordinal data (rank-ordered data) does not meet the assumptions of normality, and you cannot use an arithmetic mean to describe the central tendency—only the median.

Xander Henderson
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Kathystats
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