Filter to remove blanks doesn't work

[DataSkills]

Hi, 

I have a table of patients with Patient.ID. I then have a table of medical assessments done on said patients. I want to know which patients have NOT had a specific assessment done. 

The relationship is between Patient.Id (one) to Assessment.PatientID (many). 

If I create a table visual of Patient.Id and sum of Assessment.score, I get the following, which shows some patients with a blank score. These blank score patients are the ones I want to isolate and display. 

I thought this would simply be a case of placing a filter on the visual where score is blank. 

However, when I do that, it has no impact on the visual, other than making all the scores blank as per the image below. 

I am a bit stumped as to why this behaviour is happening and an answer on how to achieve the desired result which is to display only those patients who have not had the assessment (eg 20914, 20919, 20922, 20923 etc). 

Many thanks

[amitchandak]

@DataSkills , I think you need is not blank

[DataSkills]

Hi @amitchandak thanks for that suggestion, but changing the filter to is not blank doesn't help. 

The result after applying the is not blank filter to the scores field is: