How do I filter on tickets closed last week?

I'm working on building a dashboard for an IT Helpdesk.  I'm wanting a measure for First Call Resolution (Last Week).  How can I filter on a table column that has duplicate date fields(i.e. something like PREVIOUSWEEK(incident_metric[inc_closed_at]))?  This is all I have so far... which works but does not filter on last week's tickets only:

First Call Resolution (Last Week): = CALCULATE(COUNTA(incident_metric[mi_value]),incident_metric[mi_value]="true")/COUNTA(incident_metric[mi_value])