What was the median age for cats with inflammatory bowel disease and small cell lymphoma, and was the difference significant?

• A. IBD 7.4 years (SD 3.68); Small cell lymphoma 10.9 years (SD 3.35); P = .009
• B. IBD 10.9 years (SD 3.35); Small cell lymphoma 7.4 years (SD 3.68); P = .009
• C. IBD 7.4 years (SD 3.68); Small cell lymphoma 10.9 years (SD 3.35); P = .05
• D. IBD 6.0 years; Small cell lymphoma 9.5 years; P = .2

Answer: (A)

Comparing age at diagnosis between the two groups tests whether one disease tends to present in older cats and whether that difference is likely real rather than due to chance. The medians are 7.4 years for inflammatory bowel disease and 10.9 years for small cell lymphoma, with similar variability (SD around 3.4–3.7 years). The P value of 0.009 indicates the difference is statistically significant, meaning there’s less than a 1% chance this difference would occur if there were no true difference between the groups. In other words, small cell lymphoma tends to be diagnosed in older cats than inflammatory bowel disease, beyond what random variation would explain. Other options would swap the ages or report a non-significant P value, which doesn’t fit the data.