The Constipation Assessment Scale (CAS) consists of eight characteristics deemed on the basis of literature searching to be universally related to constipation. Each of these characteristics is given a three point rating scale ("No problem", "Some problem", "Severe problem"), scored 0, 1 or 2 respectively. These scores are summed to make a range between 0 for no constipation and 16 for the most severe constipation.

The CAS was tested for construct validity and sensitivity by comparison of results obtained on 32 normal volunteers and 32 patients receiving either morphine or vinca alkaloid chemotherapy (t = 6.32, p < 0.0001). Reliability (r = 0.98) and internal consistency (µ = 0.70) were also satisfactory. The scale was able to distinguish between more and less severely constipated groups (on the assumption that the chemotherapy patients were less constipated than those receiving morphine),( t = 2.54, p< 0.01). Completion time averaged about two minutes.