*3.1. Number of Published Items and Publication Trend*

The process of screening and selecting papers is presented in Figure 1. Among 326,405 articles about quality of life, a total of 1624 publications met the eligible criteria and was selected for further analysis.

General characteristics of the selected publications are presented in Table 2. Since 1991, when the first studies on quality of life of people suffering from asthma were published, the number of papers considering this research interest has grown gradually. The total citations of articles published during the 2000s were relatively high compared to publications in recent years. Meanwhile, the total usage, defined by the total downloads, and mean use rate during the last six months were considerable for the research in 2017 and 2018, suggesting the continuous update and rising interest in the topic recently.

**Figure 1.** Selection of papers.


**Table 2.** General characteristics of publications.

<sup>1</sup> mean cite rate per year <sup>=</sup> total citations/[total citations × (2018 − that year)]; <sup>2</sup> total usage: total downloads; <sup>3</sup> mean use rate last 6 months = total usage last 6 months/total number of papers; <sup>4</sup> mean use rate last 5 years = total usage last 5 years/(total number of papers × 5).
