# How to check if a series increases or decreases?

I work with Google Adwords. Recently Google has changed its layout regarding its ads. And I want to measure what was the impact of that change.

I don´t want to do a super analysis, but I would like to do more than just look at the chart and say: "this line goes up". I had an idea of how to measure that: however, I not very sure if it´s the correct way and if my reasoning makes sense.

We pay our ads on Google according to how many people click on the ads. It´s called CPC (cost per click). The ads appear on Google according to a bid: I compete against other people who also want to show their ads. Prior to the change in layout there were 10 spots to show ads; now there are 5.

My hypothesis is that, with fewer spots, there will be more people competing per spot, the bids will get higher and therefore my CPC will be higher.

I need to check if this is indeed the fact.

My idea is to get a time series, trace a tendency line and see the angle of this line. I have to do that for about 60 accounts. If most of the angles are positive I can deduce that the CPC has increased; if most have a angle close to zero or negative, I can deduce that there were no increases in CPC. I think I can also calculate the chi-square to see how relevant these results are.

Here is a example of the data from one account.

• Your context suggests that you would have a break in mean in the CPC time series, whereas you say that you want to discover a break in trend. These are two different things, and you should be clear on which one you want. – tchakravarty Mar 24 '16 at 19:40
• Sorry for the ignorance. But could you explain the diference? – user3347814 Mar 24 '16 at 20:23
• Everybody wants to do this (simply and probably incorrectly) . Detecting level shifts ( a form of change ) is important to your analysis. Detecting changes in trends ( a form of a change) is important to you. Both circumstances need to be robust to pulses or one-time anomalies and possible daily effects. All analyses need to be robust to the underlying auto-projective memory . Please post an example of one of your series and I will try and help. There is absolutely no quick/cheap/easy/basic/childlike procedure ... there is just a lot of deficient approaches BUT I will try and help. – IrishStat Mar 24 '16 at 20:39
• Here is a example from one account: docs.google.com/spreadsheets/d/… – user3347814 Mar 25 '16 at 1:06
• When you state I din't want to do a "super analysis" you are implicitely asking for " a back of the envelope" quick'n dirty solution that is highly unlikely to be worth anything and will deliver on average a worthless result. There is no Santa Claus for you or this problem/opportunity just complexity and extracted/useful information gleaned from the data.. – IrishStat Mar 26 '16 at 20:39