# [Relation of daily sales] Chi-Square, T-Test or Correlation?

#### kggunes

##### New Member
Hello,
Which to use to test whether Monday sales and sales on the other days of the week are independent from each other.

Case:
A promotion offered on Mondays this year, so I want to "test" if the customers are trading off. The idea is to check the relation of weekdays last year and this year. Which method do you think would fit best?

Thank you for the help in advance!

#### kggunes

##### New Member
Sorry for being unclear earlier..

The price of Product A on Mondays offered for a lower price than the rest of the weekdays in 2012 (35 Weeks). As you can guess, the unit sales of Product A is higher on Mondays compared to the rest of the week and compared to the last year. I guess in theory, under usual circumstances (e.g. without price reduction, stable consumer behavior, etc.) the sold units relation between each day (Mon vs. Tue, Mon vs. Wed, etc.) should be same in 2011 and 2012.

So, I would like to see whether customers are trading off with other days (i.e. if they are not buying the Product A on the other weekdays and wait Mondays to buy it). If this is true than results should be skewed towards Monday, isn't it? And of course, is simple correlation enough to prove this?

Hope that clears a bit..

#### kggunes

##### New Member

in 2011, the price of Product A was same in all weekdays.
in 2012, only Mondays offered for a lower price.

#### hlsmith

##### Less is more. Stay pure. Stay poor.
A good first step might be just running the 2x7 chi-sqaure and looking to see if things appear to change. Is there any seasonality in regards to the purchasing of the product. You may think to compare the same 35 weeks of the two years.

#### kggunes

##### New Member
A good first step might be just running the 2x7 chi-sqaure and looking to see if things appear to change. Is there any seasonality in regards to the purchasing of the product. You may think to compare the same 35 weeks of the two years.
Hello hlsmith,

you meant like this

........MO TU WE TH FR SA SO
2011
2012

This shows me if the years are dependent with days or not, isn't it?

#### hlsmith

##### Less is more. Stay pure. Stay poor.
Correct, this will provid you with frequency table data. It does not matter if you run 2x7 or 7x2, I thought the above presentation would allow you to better see the frequencies per day and year in an interpretable way with the naked eye. A significant p-value will inform you that a difference exists, though it won't tell you which cells are different. Subsequent tests will have to tease that out.

#### victorxstc

##### Pirate
Some things came to my mind.