Regression modelling is a popular approach for analysing epidemiological data. While its analytical techniques are widely covered by standard textbooks, modelling approaches vary between disciplines, potentially confusing many users. Identifying the motivation behind epidemiological analyses, particularly understanding of causal inference, would naturally guide users. Nevertheless, this subject has not been taught systematically in many of the veterinary epidemiology curriculums. This series of articles aim to showcase the minimum standard for regression modelling, highlighting basic concepts such as confounding. In this first article, a regression modelling approach to making causal inference is explained.