I think that there is a problem with the way that rot statistics are calculated. Essentially, I believe that the number of reports for a title is double-counted, leading to popular discs looking worse than they ought to.

This is how it seems to work at present. The scores for each rot report are added up with the following weighting:
Light: 1
Medium: 2
Strong: 3
Critical: 4
Dead: 5

So, a Medium and two Criticals would result in 10, for example. But then, that score is multiplied by the total number of rot reports (3 in this case), leading to a score of 30. This seems to me to be using the number of reports twice. It’s not “wrong” in an absolute sense, I just don’t think that it is what one might expect.

For instance, a title with one Light report scores 1, but a title with two Light reports, scores 4. I think the score should increase but not quadruple.

I also think that one should somehow use the total number of that title registered in collections for this.

Suppose 500 people have Title A in their collections. 20 of those 500 people report Medium Rot. That gets a score of 800.
Suppose 10 people have Title B in their collections and 5 of those 10 report Death. That only gets a score of 125.

If you were thinking of buying Title B, wouldn’t you be much more worried by that than the Title A case? I think the scores should reflect this.

As an immediate (but still far from perfect) improvement, I would suggest that rather than multiplying by the number of reports, multiply by the “rot vs collection” percentage, which is already calculated by the database.

I would also suggest changing the weighting for the rot severity categories a bit – something like this, perhaps?
Light: 1
Medium: 2
Strong: 4
Critical: 6
Dead: 10
I think a dead disc is more than 5 times as bad as a lightly rotted one.

Of course, I intend no negative criticism of Julien’s bloody brilliant work on the LDDB, for which we all continue to be very grateful.

All thoughts welcome and, of course, SYNW.

If you are a user with multiple copies of a particular LD where more than one may be rotted (which is surprisingly common when you have as many discs as I do), there doesn't appear to be any way to enter all of them as rotters therefore the accuracy of the rot statistics is dubious at best.

Yes, that's true too.

And if one of one's copies is rotted, and another is not, one needs to be able to report zero rot for the unrotted ones.