as per the top reply, if you want to have a standard deviation summary on the weekly data (i.e. on 10, 25, 26, 18...) then you need to have that data returned pre-aggregated at the weekly group level.
this means that you would base the report on a Command object or a stored procedure that returns the data aggregated on the weekly level.
using the screenshot you provided your new dataset should be 13 records.