Possums in five areas

Topic: Chi-squared examples · more questions on this topic
Genotype and mating success ›

Counts of possums in five areas of similar size and habitat are 234, 301, 256, 315 and 274.

1. What are the expected counts if every area is equally attractive?

2. Compute the Pearson statistic.

3. Under the null hypothesis the statistic is approximately \chi^2_4. The upper tail beyond 15.63 is 0.0036. What is the conclusion at level 0.05?

Worked answer (click to show)

The total is 1380, so each expected count is 1380/5=276. The Pearson statistic is

\sum\frac{(O_i-276)^2}{276}=15.63.

The approximate null distribution is \chi^2_4. The p-value 0.0036 rejects equal attractiveness at level 0.05. Some areas are preferred.