Or you could group on {Caseinfo.CaseName} and then create a formula {@unknown}:
if {Injury.InjuryType} = "Unknown" then 1 else 0
Place this in your details section.
If your goal is just to exclude cases with any injury identified as "unknown", then place this formula in your group select statement:
Sum({@unknown},{Caseinfo.CaseName}) = 0
You will then need to use running totals for calculations with the remaining data, since the excluded cases would still enter into the more usual summaries, e.g., counts, etc.
If your goal is to both exlude cases with "unknown" as an injury and to select cases with a specific injury, try this formula {@injury} in the details section:
if {Injury.InjuryType} = "Unknown" then 1 else
if {Injury.InjuryType} = "Stroke" then 1000 else 0
Then in your group select, use:
remainder(sum({@injury},{Caseinfo.Casename}),1000)= 0
This would select casenames which have "stroke" but not "unknown." You could also create a parameter {?injury} and plug that into your formula instead of "stroke" so you could check the data for selected injuries of interest.
-LB