**3. Results**

The worldwide search query using Google TrendsTM highlighted a decrease from an index of 76.3 in 2004 to 25.4 in 2018 (absolute reduction −50.9, or a relative reduction of −66.7%, see Figure 1). This trend was particularly confirmed in the US, with a decrease of the Google TrendsTM index from an index of 68.4 to 17.0 (absolute reduction −51.4, relative reduction of −75.2%) over time. While an initial sharp decrease in search results was observed from an index of 68.4 to 37.6 (absolute reduction −30.8, relative reduction of −45.0%) within two years, there was a further decrease by 54.8% over the following thirteen years. In the same period of time, UNOS reported an increase of deceased donor kidney transplants from 16,007 in 2004 to 21,167 in 2018 (+32.2%); within the same period the live donor kidney transplantation rate remained stable (6648 in 2004 and 6442 in 2018, −3.1%). A similar search tendency of a decreased Google TrendsTM index was found for the Eurotransplant area and the UK. There was a modest increase in Google TrendsTM search queries in Spain, with a very low number in 2004 (index of 8.3) and 10.1 in 2018 (absolute increase +1.8, or a relative increase of +21.7%). In the same time-period the number of transplanted kidneys increased from 2125 to 3313 (+55.9%). In smaller countries, it is likely that events of interest to the public lead to an increase in search queries in that particular year. This for example might explain the increase in search queries in Austria in 2005 when a person of public interest received a second live-related kidney transplant in the same year. We observed an increase of Google TrendsTM search queries from an index of 26.3 in 2004 to 36.6 in 2005 (absolute increase +10.3 or relative increase of +39.2%). In the following years, a decrease was found with an index of 12.9 in 2018 (absolute reduction −13.4 or a relative decrease of −51.0%). Similar curves were observed in all Eurotransplant countries, even in countries with a higher number of live-related kidney transplants, for example, the Netherlands (48.1% in 2004 and 40.0% in 2018), where more web-based information retrieval might be expected. Online searches assessed by Google TrendsTM decreased from 49.3 to 37.8 (−11.5, or −23.3%) over 15 years. In Germany a decrease from 52.4 to 30.7 (−21.7, or −41.4%) was found in the same period, with even more pronounced reductions observed in Belgium (from 21.5 to 8.1, corresponding to a decrease of 13.4, or −62.3%) and Hungary (from 8.3 to 2.6, absolute reduction of −5.7 or relative reduction by −68.7%). In the UK, Google TrendsTM indices decreased from 33.25 to 7.58 with an absolute reduction of 25.67 and a relative reduction of −77.2%, mirroring the decrease observed in the US. An overview of Google TrendsTM changes over time and number of transplants (deceased donor and live donor transplantation) in the respective countries is highlighted in Table 1*,* Table S2, and Figure 2.

**Figure 1.** A worldwide decrease in the Google TrendsTM indices from inception to 2018 was found. During a period of 15 years, the index decreased from 76.3 to 25.4, corresponding to a change of −66.7%.

We used correlation analysis to compare the Google TrendsTM indices to the number of transplants over time and found negative correlations in particular for the UK, Belgium, and Austria, but also for Hungary, Slovenia, Germany, and the US. Spain is the only country where both transplant numbers as well as Google TrendsTM indices show positive correlations above 0.5 (Figure 3).


**Table 1.** The respective year, number of search queries using Google TrendsTM, and the total number of kidney transplantations performed (deceased donor and living donor). Abbreviations: GT (Google TrendsTM), US (United States of America), UK (United Kingdom), ESP (Spain), B (Belgium), NL (the Netherlands), GER (Germany), AUT (Austria), SLO (Slovenia), H (Hungary), CRO (Croatia), Tx. (transplants).

**Figure 2.** The respective numbers of renal transplants (red line) and the Google TrendsTM indices (blue line) are given for the United Nations of Organ Sharing (UNOS), the Organización Nacional de Trasplantes (ONT), the Eurotransplant areas, and the UK National Register. Numbers of deceased and living donor transplants are indicated by light and dark red areas. While there was a marginal increase in the Google TrendsTM index observed in Spain, the curves obtained from the UNOS, Eurotransplant areas, and the UK National Register mirror the worldwide trend.

**Figure 3.** Time-lag correlations of Google TrendsTM indices and number of performed transplants for the countries under study. Negative correlations between Google TrendsTM indices and number of transplants are highlighted in green to blue whereas positive correlations are given in orange to red.
