The Chi-Squared Test

Today a charge nurse explained to me why patients admitted as emergencies in the late afternoon and evening will tend to stay in the admissions ward longer than the patients admitted at other times of the day (it's to do with the timing of ward rounds). I'm not a man to take such a hypothesis on trust so I got the data and calculated a P value using the chi-squared test: P = 0.0024. Statistically significant.