Query Results - Not Getting Different Values Returned For Each Row

I am getting the following results from my query that contains a subquery, but I don't understand why the values in the [Total Volume M_Active_Previous] are being repeated with the same value. I should be getting different values returned for each row like in the [Total Volume M_Active] column.

Why the values are all the same and how I can fix this?

DayNoDayTotal Volume M_ActiveTotal Volume M_Active_Previous
6 Friday11161 72491
7 Saturday5687 72491
2 Monday14354 72491
1 Sunday3966 72491
4 Wednesday12340 72491
3 Tuesday12018 72491
5 Thursday11833 72491

Here is the SQL I'm using.

Code:
DECLARE @StartDate datetime, @EndDate datetime, @Prev_StartDate datetime, @Prev_EndDate datetime
SET @StartDate = '2011-03-13 00:00:00.000'
SET @EndDate = '2011-03-19 23:59:59.999'
SET @Prev_StartDate = '2011-03-06 00:00:00.000'
SET @Prev_EndDate = '2011-03-12 23:59:59.999'

[Code] ....