In the absence of a gold standard for the diagnosis or treatment of a disease, doctors have difficulties diagnosing and treating patients. In order to solve these problems, clinical studies are conducted. Clinical studies have various possible methodologies, and randomized controlled trials (RCTs) are especially reliable. A meta-analysis is a collection and analysis of the results of RCTs on a given topic [4]. Meta-analyses have the advantage of overcoming the limitations of individual studies and obtaining generalizable and objective results. However, since meta-analyses are studies of existing studies, a potential problem is that they are affected by the quality of existing studies. In addition, meta-analyses have been criticized for mixing heterogeneous studies together and analyzing them, as if comparing apples to oranges. In order to overcome these problems, researchers must produce integrated and objective results by minimizing the errors that can occur in the meta-analysis process. In my opinion, the 2 letters about the article “Role of Transcutaneous Electrical Nerve Stimulation in Treating Children With Overactive Bladder From Pooled Analysis of 8 Randomized Controlled Trials” reflect an effort to overcome the problems that may occur during meta-analysis [5,6].

The results of research published on the human microbiome are often difficult to compare because of differences in study design, and many problems remain to be solved. The letter that Professor Lee sent regarding the article “The Urine Microbiome of Healthy Men and Women Differs by Urine Collection Method” contains an insightful description of future challenges facing research into the human urinary microbiome [7].

Professor Kim sent the letter about health disparities during the COVID-19 pandemic [8]. I hope the day will come when COVID-19 disappears quickly on Earth.

On behalf of the Editorial Board of INJ, I would like to thank all the authors who wrote letters for the June issue of INJ.