Preceding studies found that clinicians using the Traditional Diagnostic Assessment (TDA, the standard of clinical practice) often made imprecise diagnoses, compared with gold standards. Those same studies found excellent diagnostic agreement (kappa>0.75) between Computer Assisted Diagnostic Interview (CADI) and gold standards, thus warranting CADI's use as the standard for data collection and diagnosis in this study. When TDA and CADI users independently examined 106 inpatient-subjects, TDA users agreed only 45.3% (48/106) with CADI's primary diagnosis and found only 50.5% as many total diagnoses. This study searched for the causes and effects of those differences. To test the hypothesis that insufficient data collection was the cause, the 106 TDA write-ups were analyzed word-by-word. Only 46.2% (49/106) of the TDA write-ups listed enough symptom criteria (e.g. hallucinations, depression) to meet DSM-IV requirements for diagnosis, a likely cause of TDA's inaccuracy. TDA write-ups evaluated only 52.9% of the 18 Key Criteria necessary to screen for 10 diagnostic groups, a likely cause of TDA's incompleteness. TDA's diagnostic imprecision had effects on (1) length of stay (LOS) for hospitalized patients and (2) associated costs. Patients evaluated with TDA had a mean LOS of 12.5 days versus 7.7 days for CADI patients, a reduction of 4.8 days (12.5-7.7). If CADI replaced TDA, then annual savings of 3,000,000 dollars system-wide could be projected for inpatient care. Remedies for TDA's diagnostic imprecision are proposed.