Letters to the Editor Re: Breyer et al.: Use of Google Insights for Search to Track Seasonal and Geographic Kidney Stone Incidence in the United States (Urology 2011;78:267-271) TO THE EDITOR: We read with great interest your article “Use of Google Insights for Search to Track Seasonal and Geographic Kid- ney Stone Incidence in the United States” by Breyer et al. They noted that when they entered the query “kidney stones” into Google Insights for Search, the curve showing the popularity of this Google query over time has approxi- mately the same shape as the curve for hospital admissions for kidney stones. Similarly, the geographic distribution of Google searches for “kidney stones” is similar to that of hospital admissions for this condition. The authors state that “kidney stones” was the best search term they found to mirror the hospital admission data. They determined this by guessing search terms and entering them into Google Insights for Search. We think there may be better correlated terms and certainly some more surprising ones. A recently launched tool called Google Correlate allows anyone to systematically look for search queries that have the same pattern over time (or geography) as any other search query, or even any other dataset. In this case, entering “kidney stones” into Google Cor- relate shows that “lower abdominal pain,” “back pain,” and “burning sensation” are all highly correlated with the query “kidney stones” over time (http://www.google.com/trends/ correlate/search?e=kidney+stones&e=lower+abdominal+ pain&t =weekly#). One can also determine which queries best correlate with the actual kidney stone hospital admis- sion data without first having to guess the query: simply upload the dataset to Google Correlate and see what queries are returned. We do not have access to the dataset so we cannot try this ourselves, but we look forward to learning about what others discover. Roni Zeiger, M.D., and Matthew H. Mohebbi Google, Inc. Mountain View, California Reply by the Authors TO THE EDITOR: We greatly appreciate the interest in our manuscript. 1 Our findings, teamed with our previous research, 2 and an out- standing report by the group from Tucson, Arizona, 3 all demonstrate that Internet search volume can track kidney stone incidence. The authors of the letter are mistaken when they assert that we selected search terms by guessing. Terms associated with kidney stones were selected and analyzed based on clinical experience and knowledge. In Google Correlate, Google has once again produced a useful tool for researchers. We imagine that it will be put to work by researchers around the globe for useful purposes. Our initial perusal of the site returned results that were insightful, ironic, and humorous. For example, the most correlated term with “Prostatectomy” was vas- culitis (r = .9111). 4 Although Gleason score (r = .8956) and urinary incontinence (r = .8743) were included in the top 10 terms correlated with prostatectomy, so were malt lymphoma (r = .8796), synovitis (r = .8791), and lymphocytic (r = .8759). Fortunately for our urological oncology colleagues, erectile dysfunction was not one of the top 10 correlated terms with prostatectomy. Google Correlate also produced some humorous health- related results. The phrase with the highest correlation to the health term “testicles” was “cast of full house” (r = .8722), a popular 1980s sitcom. 5 Also in the top 10, “Taylor Swift Innocent lyrics”(r = .8514), a popular music song with no direct or obvious connection to the term “testicles.” Benjamin N. Breyer, M.D., M.A. Michael L. Eisenberg, M.D. Department of Urology University of California San Francisco, California References 1. Breyer BN, Sen S, Aaronson DS, et al. Use of Google insights for search to track seasonal and geographic kidney stone incidence in the United States. Urology. 2011;78:267-271. 2. Breyer BN, Eisenberg ML. Use of Google in study of noninfectious medical conditions. Epidemiology. 2010;21:584-585. 3. Willard SD, Nguyen MM. Internet search trends analysis tools can provide real-time data on kidney stone disease in the United States. Urology. In press. 4. Google Correlate. Term searched: Prostatectomy. Available at: http://www.google.com/trends/correlate/search?e=prostatectomy&t= all#. Accessed October 19, 2011. 5. Google Correlate. Term searched: Testicles. Available at: http://www. google.com/trends/correlate/search?e=testicles&t=all#. Accessed Oc- tober 19, 2011. Re: Graft Reconstruction of Inferior Vena Cava for Renal Cell Carcinoma Stage pT3b or Greater (Urology 2011;78:838-843) TO THE EDITOR: The authors report their surgical experience of graft re- construction of the inferior vena cava (IVC) after resec- 486 © 2012 Elsevier Inc. UROLOGY 79: 486, 2012 • 0090-4295/12/$36.00 All Rights Reserved doi:10.1016/j.urology.2011.10.063