Since the nineties there has seen a striking increase in the number of compulsory admissions in the Netherlands. Van der Post and colleagues aimed to highlight changes in emergency psychiatry in Amsterdam which have contributed to the rise in the number of acute compulsory admissions. They compared a cohort of consultations conducted by the city crisis service in 1983 (n = 460) with a similar cohort of consultations conducted in 2004-2005 (n = 436).

Results showed that the total number of admissions following a consultation decreased, but there was a rise in the percentage of compulsory admissions. The researchers used a Chi-square test to evaluate the differences in the number of voluntary and compulsory admissions between 1983 and 2004-2005. This is a test of equal distribution of the number of admissions across judicial status and cohort. However, this is not a useful comparison. The null-hypothesis of no difference is unlikely, if not impossible, given the observed increase in the number of compulsory admissions. That number more than doubled per 10.000 inhabitants in this high density urban area. Yet in the Chi-square test the absolute difference in the number of acute compulsory admissions in 1983 and 2004-2005 was only 78 and 87 respectively. Probably the selection of the 2004-2005 cohort was biased in an effort to select cases based on the criteria used in the 1983 cohort. In any case, the calculated P-value of the Chi-square test is not helpful.