Using the equals(=) operator when referencing a date to a number in an IF statement

I am looking to create a numeric formula field in a table.  I am looking to define a specific number based on the date in a field called "Period Tested".  For example:

If Period Tested = 01-01-2016, display the number "1"
If Period Tested = 02-01-2016, display the number "4"
etc.

I've written it out as such:

If([Period Tested]="01-01-2016",1,
[Period Tested]="02-01-2016",4)

I am using the Formula - Number type for the field.

I get the following error when I try to save:

The expression [Period Tested] on the left hand side of the operator "=" is of type date while the expression "01-01-2016" on the right hand side is of type text. The operator "=" cannot be used with these types of expressions.

I'm not sure how to circumvent that in the system exactly, but I need the final number to show based on the date from the Period Tested field.  Any idea how I can work around this?  I looked a bit and didn't find any operator that could replace the equals(=) in this scenario.  

Thanks for your time!