This icon means a spec constitues less than 1% of the samples seen and the values may not be statistically reliable. These specs are hidden by default.
There are a few things to be aware of above all else:
Spec Score is the best measure I've been able to come up with to compare specs across all fights of a given tier. The goal has been to minimize the effect a "gimmick" fight has on the overall rankings and generally normalize fights to have a common ground of comparison.
In a nutshell, each spec is scored on a curve for each fight. For each individual boss, the spec with the top DPS on a fight gets a score of 100 and then all other specs are scored according to that top spec. The average across all fights for a given spec is the Spec Score for the current tier.
As usual, this score is not the end-all, be-all measure of anything. It's merely an interesting collection of data trying to compress a whole lot of data into a single comparable value. Don't ever forget that each spec has its strengths and weaknesses and may be needed for any number of reasons. While raw numbers are absolutely an important facet of raiding, there are often other variables that are far more important.
All of that said, I think Spec Score is a far better indicator of relative spec power than a simple aggregation of DPS values from all fights. Those values are still available but I hope and pray that you understand that they have their own variety of problems and caveats.
A more detailed description and example will be posted on the Raidbots Blog.
More details of the methodology used can be found on the DPS Bot Docs page.
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Feel free to contact me via the Raidbots Blog or directly via email
sollaires at gmail dot com