Does it Matter Which Citation Tool is Used to Compare the h-index of a Group of Highly Cited Researchers?

H-index retrieved by citation indexes (Scopus, Google scholar, and Web ofScience) is used to measure the scientific performance and the researchimpactstudies based on the number of publications and citations of a scientist. Italso is easily available and may be used for performance measures ofscientists, and for recruitment decisions. The aim of this study is toinvestigate the difference between the outputs and results from these threecitation databases namely Scopus, Google Scholar, and Web of Science based uponthe h-index of a group of highly cited researchers (Nobel Prize winnerscientist). The purposive sampling method was adopted to collect the requireddata. The results showed that there is a significant difference in the h-indexbetween three citation indexes of Scopus, Google scholar, and Web of Science;the Google scholar h-index was more than the h-index in two other databases. Itwas also concluded that there is a significant positive relationship betweenh-indices based on Google scholar and Scopus. The citation indexes of Scopus,Google scholar, and Web of Science may be useful for evaluating h-index ofscientists but they have some limitations as well.