Why are my keyword rankings dramatically changing week to week?

[SummitCom]

I have a site (actual several) that has been up for many years now. Content is changed monthly - regularly. It would always rank in the top 5 positions for 5 or 6 keywords.

Now all of a sudden (without any dramatic changes to the website) my ranking results from my weekly Moz reports are dramatically different from week to week - every week. One Keyword will be #1, then the next week it will drop 49 positions, the 3rd week it might be #5, then Not in the Top 50, then #1 again, and so and so on. This happens to all my keywords on my site.

I was waiting for Google to finish it's changes to it's algorithms but it's now been long enough and I can't get a handle on what's happening, why it's happening, and what to do about it, and what direction to take with my SEO.

My Traffic has actually improved over last year by approx. 25%, but I have also started a PPC campaign for this client.

Any suggestions would be great.

[SummitCom]

Thanks for your responses. I looked at everything using your suggestions and I just think that my wild fluctuations are real. I used the Rank Tracker tool on Keywords on my competitors for a long while now, and it shows what I felt, that starting back in April through around June 2013, Google started messing with everything. Around 45 Keywords are all over the place since then- one week they rank 50+ the next week #1, etc. Before that pretty much of a straight line. I think Moz reports are sometimes off a little, but in these cases it's pretty accurate. I've tracked in Moz Rank Tracker for a couple of years my 5 main competitors, they now are barely on any page in the top 50, and the Rank Tracker proves it.

I've even done just a manual search and counted the positions - and it's fairly accurate. I just can't figure out what to do now in Google to get a consistent score and a consistent good score. All my pages grade A for the specific keywords I want, and they have always ranked for several years in the top 5. Now it's just all over the place.

Just can't figure it out.

Thank you for your input. I was trying several things to see if I could get a change, before I replied, but no joy.

[Kingof5]

We have wild fluctuations like that for our sites every week, and many of them are not accurate when checked manually - sometimes they're more than 10 positions off. And then sometimes the changes as showing it out of the top 50 is completely wrong.

A Moz team member looked at our campaigns said we just have highly volatile keywords. That seems kind of ridiculous to me, it's not like we're in a super super competitive niche.

[MikeRoberts]

Have you double-checked your rankings either through another tool or through unpersonalized searches to see if the Moz data is correct? I have a few search terms on two of my campaigns that regularly swing from 1st one week to "Not in top 50" the next according to Moz when in reality they barely shift ever.