Clinical epidemiology is defined as a method for investigating the distribution and determinants of diseases and for applying this knowledge in their prevention, and simply means application of epidemiological methods for medical research. In evidence-based medicine, randomized controlled trials (RCT) are the gold standard for assessing efficacy and safety of the intervention, while it is commonly impractical because of many limitations, such as ethical/legal problems and weak external-validity. High internal-validity of RCT permits to assess the direct efficacy of intervention without interference with bias and confounder; however, it has less generalizability or applicability to the real-life practice. Evidence-based practical guidelines are developed for patient management and decision making in real-life practice; paradoxically, the evidence of the guidelines does not come from real life, but from strict trial life. To overcome these limitations, pragmatic clinical trials for assessing the effectiveness of intervention in real-life practice or high-quality observational studies would be the best alternatives or could add more strong evidence. This article provides an overview of clinicoepidemiological research designs in the field of childhood allergic diseases and their strength/weakness. (Allergy Asthma Respir Dis 2016;4:91-99)