(See How is an MAU instrument validated.)

In sum, this involves 4 separate issues:

• The validity of the utility measurement or scaling technique (TTO, SG, PTO, RS);
• The validity of questionnaires or descriptive systems; 
• The validity of the model which combines items; and
• Evidence that final instrument scores have an interval and strong interval property.

The claim that an instrument ‘has been validated’ generally rests upon context specific tests of the second property. However correlations found in these studies do not represent strong evidence of general validity (see Does correlation demonstrate validity). The low correlation between the major MAU scales in use demonstrates that some or most or all lack content validity across all contexts.