The authors investigated the link between patient characteristics, the Camberwell Assessment of Need Short Appraisal Schedule (cansas), early drop-out and treatment duration. Results showed that patients with severe mental illness (smi) who remained under treatment by an assertive community treatment team (N=611) were more frequently male, born outside the Netherlands and had a psychotic or addiction disorder more frequently than patients who had left the act team treatment early (N=430).

Table 1 (see below) shows that 62% of the patients born outside the Netherlands remained in treatment versus 38% drop-outs. That looks like a large 24% difference. However, patient characteristics were summarized in misleading row percentages.

The conclusion that patients who remained under treatment were more frequently born outside the Netherlands is based on 10% difference: 55% versus 45%. Proportions of drop-outs were even closer: 45% natives versus 38% of patients born outside the Netherlands. What looked like a 24% difference is only a 7% difference.



  In care Drop out    
Dutch 272 221 493  
Non-Dutch 339 209 548  
  611 430 1041  
Column 44,5% 51,4% 6,9%  
  55,5% 48,6% 6,9%  
Row 55,2% 44,8% 10,3%  
  61,9% 38,1% 23,7%  


The authors reported no effect sizes, but the link between ethnicity and drop-out can be expressed as an odds ratio: 1,32, 95% confidence interval: 1,03-1,69. This odds ratio is statistically significant, but that is no surprise when N=1041. Mulder and Kortrijk conclude that information on patient characteristics is important for the correct interpretation of routine outcome monitoring data. However, they failed to show the relevance of a 1,3 odds ratio.


Also see Mulder and Kortrijk need some benchmarking 

Mulder CL, Kortrijk HE. Effects of treatment duration on the interpretation of rom data in a c t patients. Tijdschrift voor psychiatrie, 54(2012)2, 191-196.