Webmaster Tools vs. Google Trends data doesn't add up

[WillW]

I am investigating a two-month 25% drop in organic traffic from Google to a client's site.  When I turned to the Webmaster Tools data for the site, there is a clear, gradual drop over the course of a couple months both in impressions and clicks.  In general, the drop occurred across many pages and for a large number of queries; there wasn't a core group of keywords or pages that saw the drop...it was more sitewide.  Yet, the average rankings reported by WMT were, for the top 100 or so landing pages, not significantly different.

The site hosts information about medical conditions, and I wouldn't expect any time-related variations in search volume, and this was confirmed by looking at Google Trends data for a number of the top keywords.  I started to look at the data by query for all the top keywords (all ranked in the top 10), and saw the following general trend:  impressions were down, rankings stayed in the top 10, and Google Trends showed either flat or rising volumes.

So I am trying to make sense of that.  If the search volume trend did not decline and rankings held inside the top 10, then how could the number of impressions drop significantly?  Am I trusting the WMT data too much?  But the reality is that the volume of traffic measured by Google Analytics from Google organic did indeed drop the way Webmaster Tools show it.

[evolvingSEO]

You're welcome! One last suggestion I'd make is if you have the budget, to augment Moz rankings with daily rank tracking. Weekly might be enough, but if you want to turn it up a notch try Authority Labs. I find them accurate and robust for daily rank tracking.

[WillW]

We have WMT data monthly, and are setting up a Moz campaign for the site so that we'll have weekly de-personalized data moving forward.  Will also take a look at the SEMrush data.  Thanks for the suggestions.

[evolvingSEO]

Also, you can try to see if SEMrush has any past ranking data - depending on the volumes, you might find something: http://www.semrush.com/

[evolvingSEO]

I wouldn't call it inaccurate, it just operates a bit different. For example;

• It's only when a page ranks - the "avg position" is only when someone actually searched, and the page ranked somewhere - it does not calculate a hypothetical ranking
• It's averaged over time periods - when you are looking at average ranking - the time period can muddy numbers. Shifting in actual ranking over 2-3 months might show an "average" position of 5, but actual could have been 5, 2, 7, 15, 1, 6, etc over time
• It's averages for logged in, logged out, search plus your world etc - rank checkers give a constant number based upon trying to de-personalize. But WMT is averaging personalized rankings, G+ "search plus your world", localized rankings etc - which is a muddy number as well.

In short - tracking rankings give you a steady ranking eliminating changing variables. I'm sure WMT is accurate, but there's a lot more moving parts so it's suspect to these things and can not be looked at as "rankings" but rather an actual look at where you happened to rank when a page did show up in someone's search.

[WillW]

For that time period we don't have a second source of rankings data.  Should there be reason to believe that the Webmaster Tools ranking data is not accurate?

[evolvingSEO]

I think your first step should be to verify rankings with another tool. Hopefully you've tracked rankings somewhere else? Do you see any changes there?