When I started doing analytics for my first large retailer, I was introduced to a concept that I had never put much thought into.
Weekly sales cycles.
Most people would quickly realize that most businesses have yearly sales cycles. This is especially true for specialty retailers. Stores that sell snowboards sell more in the winter. Swim trunks don’t sell that well in the winter…
People also have weekly habits of when they go shopping during the week.
This is compounded by the fact that when looking at sales year over year, the days of the week don’t line up. To do any sort of This Year vs Last Year (TY/LY) analysis, adjustments need to be made to the comparison range.
When To Use a Day to Day Comparison
The general rule to use a day to day or weekday to weekday comparison is if the comparison period is 7 days or less.
The following is assuming that you don’t have a monthly sales cycle that causes your customers to buy more on the first of the month.
If you were comparing sales MTD for October 2019 and you were only looking at the first 4 days of the month, you wouldn’t compare it to the first 4 days of the same month LY. You would instead compare it to the corresponding days of the week of LY.
This way, you’re comparing Tuesday to Friday to Tuesday to Friday. 10/1/2019 – 10/4/2019 to 10/2/2018 – 10/5/2018.
When To Use a Date To Date Comparison
Following along from the above example, you would continue to use day to day until you reach October 8th.
On the 8th day, you switch to using date to date. Your comparison period would then be 10/1/2019 – 10/8/2019 to 10/1/2018 -10/8/2018.
Setting Your Comparison Period in Data Studio
Unfortunately there’s no default setting to make the change automatically once you hit the 8th day. What you need to do instead, is to break out Day to Day and Date to Date reporting on different sheets.
Since Google’s default TY/LY comparison is Date to Date, build all of your MTD, QTD, and YTD using the default TY/LY settings.
Now let’s assume that you have a dashboard that goes out every morning with the above mentioned metrics AND a look at only yesterday. You’ll have to set an “advanced” comparison date range to compare Day to Day.
Only Yesterday Day to Day Comparison
In this scenario, you’re going to want to set your default date range to yesterday. Then click on all charts and fields on your report and click “Comparison date range”. Then click “Advanced”.
For this example, you’ll want to set the comparison range to today minus 365 days. Since you’re looking at yesterday’s metrics when the report goes out today, the comparison will be 366 days. And that’s how you get to a Day to Day comparison.
Last Week Day to Day Comparison
Assuming Monday is the reporting hell for you like it is to me. You’re going to have many Monday reports that look back on the last week. To do a longer period of time like a week, it’s almost the same process.
Set your default date range to “Last week (starts Sunday)”, assuming you use a Sunday to Saturday week like me.
Next, for your comparison period. Set it to today minus 53 weeks with the appropriate start day.
And that’s it. If I missed anything or you want to know more, let me know in the comments!
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