Quite often in veterinary, and in cattle practice, we rely on support from the diagnostic and laboratory services. The interpretation of these test results is not always straight forward, and an appreciation of some of basic epidemiological principles can be useful. A lot of the work of bovine practitioner relies on diagnosing the problem/condition/ disease at hand with accuracy and confidence. Another important quantitative measure is the risk difference, or attributable risk, which tells us that, out of the 12.5% of aborting cows, 9.1% were attributable to N. caninum and the remainder due to other causes. A basic understanding of epidemiological concepts can help direct and shape the diagnostic pathway in cattle practice investigations. Effective sampling in the diagnosis of diseases in cattle practice is cost‐beffective and ensures that, within defined statistical boundaries, the sample size has ‘power’ to be confident that the conditions in question are not missed.