Mini MCAT passage: Neutrophil proliferation and disease

An epidemiologist studies the outbreak of a disease in a remote population. Preliminary studies show that about half of the population is affected by the disease. It usually lasts about two weeks, and consists of nausea, bloody diarrhea, and exhaustion.

The epidemiologist suspects that the disease may have something to do with malfunctioning of the immune system. In order to test this hypothesis, he takes measurements of white blood cell concentrations in people who have been affected by the disease and people who have not. Out of a population of $200$‍, $93$‍ report having been affected within the last $12$‍ months, and $107$‍ do not. The results are shown below:

Mean neutrophil concentration in blood:

The epidemiologist did a statistical analysis of the results and found a p-value of p = $0.02$‍. A p-value determines the probability that a result would be found if there were no association between the independent and dependent variables. In this experiment, a result is considered statistically significant if p < $0.05$‍. The epidemiologist therefore determines that neutrophil proliferation is a likely cause of the symptoms seen in the disease.