In this work, the membership ratio of RR Lyrae (RRL) variable stars in 20 globular clusters were calculated. In addition to cluster age and metallicity, which were previously known as the two main factors of star cluster evolution, this work reveals the significance of the cluster radius. Globular clusters are dense, low-metallicity star clusters. These objects are home to most RRL variables, which are important in determining the evolution of star clusters. Although considerable research has been devoted to discussing their period and luminosities, the membership ratio of RRLs within globular clusters remains an area of investigation. Using the GAIA Data Release 3 database, the apparent dimension of the clusters and an estimated number of observed stars in the clusters were calculated. Then, the membership ratio of RRLs in 20 globular clusters was analyzed. Variables combining the effect of the three key parameters were defined and used in a regression analysis. It is concluded that three factors play an essential role in deciding the ratio of RRLs to the number of stars in the home cluster, which are the cluster age, cluster radius, and metallicity, listed in order of descending correlation. Age and metallicity are negatively correlated with the membership ratio of RRLs, while radius is positively correlated to it. By discussing the clusters M54 and M10, the formation of RRLs is believed to be correlated with the home galaxy and the cluster formation history. Additionally, the negative correlation of metallicity with the membership ratio signify that RRLs are more likely to form in metal-poor environments. Given the positive correlation between the membership ratio and cluster radius, it is hypothesized that the formation of RRLs is correlated with tidal forces and properties of the home galaxy.