People who use Google Analytics are generally familiar with the ‘compare dates’ feature that lets you set up comparisons to visualize how your site is doing over time. This is especially useful if your business has peaks, promotions, etc. that don’t start on the same day each year – you can enter very specific dates and Google will overlay the performance figures, with the chart visualisation comparing your chosen time periods nicely.
Comparing date ranges in AdWords was missed by a lot of people – initially because it just wasn’t there. More recently it was added but it was sort of hidden away. Now AdWords is updated with a date selection tool including ‘compare dates’ options, almost exactly like Analytics.
This sort of thing helps businesses keep their agencies honest – you don’t need to rely on your agency’s reports 100%. Occasionally every account owner should do some basic performance comparisons on their own; looking at changes in total conversions and cost per conversion, then considering these based on business factors like client value, lifetime value, expected attrition and competitive factors.