JD_Toims - 4:09 pm on Nov 18, 2013 (gmt 0)
Percentages don't tell the whole story
IF the majority of the algorithm changes affects commercial search queries, then the percentage of sites affected within the commercial group might be vastly higher. Thus, from the point of view of commercial sites, the SERPs might be viewed as unstable.
Also, we don't know the overlap of the SERPs the % applies to, meaning it could be two consecutive changes applied to a single "niche" or "query type", but otoh, although highly unlikely imo, there may be 0 overlap in any consecutive "minor" change.
If we look at what would happen with 500+ algo updates a year and non-overlapping changes [Meaning: Change B does not affect the same SERPs as Change A; Change C does not affect the same SERPs as Change A or B; etc.] and use 0.5% of SERPs affected to a significant degree as an "average", we get:
1.37 ave. changes per day * 0.5% of SERPs affected = 0.68% of SERPs change per day
0.68% * 10 = 6.8% of SERPs change every 10 days
Approx. every 17 days and 15 hours we see a 12% overall change (Panda Size)
Every 147 days there's a 100% change to the SERPs
I know I'm using "simple math" and not accounting for the 15% of queries being new in any way, but the point is without knowing the overlap of the changes or the exact % we can't determine overall stability based on the info we have, because the entire index could [in theory at least] change in less than 150 days, even with each update/adjustment only affecting 0.5% of the SERPs.