of dementia diagnoses recorded in SIDIAP: it was cost-prohibitive to search for cases in persons with no recorded dementia diagnosis in SIDIAP. However, sensitivity has been reported to be less crucial than PPV in evaluating the accuracy of routinely collected health data, because the effects of false negatives would be diluted among the large control population.10 Moreover, our prevalence estimates were quite similar to those reported by clinical studies in Spain during the last decade, and a decreasing trend in prevalence figures has been observed in high-income countries.42 All this suggests that the recording of dementia diagnoses in SIDIAP is satisfactory. Fourth, we did not use free text to improve identification of persons with dementia. However, we used a mixed definition of dementia cases that included diagnosis and prescription or billing codes involving not only data from the general practitioner but also from the pharmacy-invoicing database. Using two different Clinical Epidemiology downloaded from https://www.dovepress.com/ by 76.229.153.206 on 05-Dec-2021 For personal use only. Powered by TCPDF (www.tcpdf.org) Clinical Epidemiology 2019:11 submit your manuscript | www.dovepress.com Dovepress Dovepress 225 Ponjoan et al data sources minimized the possible effect of underrecording of dementia diagnoses in SIDIAP. Finally, a lower education level has been associated with a greater risk of dementia.50 We could not stratify the results according to literacy, since this information is unavailable in SIDIAP. Our study has several strengths. First, it included about 10,000 incident cases in 1 year and 63,000 prevalent cases, while most epidemiological studies on dementia conducted in Western Europe had smaller samples.1 Second, our study did not depend on participants’ response rate, and thus was not affected by selection bias due to lack of response, which can be common among people with dementia due to reluctance of relatives to participate or difficulties in completing the questionnaires.1 Finally, this was a nationwide study that included >1 million people in Catalonia, a 32,000 km2 region of southern Europe. Therefore, this study provides better representation of the Spanish population than previous studies conducted in a single city5,34,44,51 or a limited area. The nationwide approach may facilitate the design and implementation of new dementia policies in national health systems. Conclusion Dementia diagnoses recorded in the SIDIAP database are valid to be used for research purposes. Age- and sex-standardized prevalence and incidence rates of dementia in 2016 were higher for women and the oldest-old population. Our figures were in line with the most recent studies conducted in Spain and higher than those provided by other primary-care databases from other European countries. These findings may be helpful to plan dementia policies not only in primary-care settings but also in secondary care and in the overall public health system. Acknowledgments We thank the Registre del Conjunt Mínim de Bases de Dades (CMBD), Divisió de Registres de Demanda i d’Activitat, Àrea de Serveis i Qualitat, Servei Català de la Salut for providing data on hospital discharges. We also thank Eduardo Hermosilla for data-management support and Elaine Lilly for revision of the English text. This work was supported by the Real world Outcomes across the Alzheimer’s Disease spectrum for better care: Multi-modal data Access Platform (ROADMAP) from the Innovative Medicines Initiative (grant agreement 116020). This project was also supported by clinical research grants from Carlos III Health Institute, within the Net for Research in Preventive Activities and Health Enhancement (RedIAPP RD16/0007/0004) framework, and from the Agency for Management of University and Research Grants (2017 SGR 1146). Disclosure The authors report no conflicts of interest in this work. References 1. Martin Prince A, Wimo A, Guerchet M. World Alzheimer report 2015 the global impact of dementia an analysis of prevalence, incidence, cost and trends; 2015. Available from: https://www.alz.co.uk/research/ WorldAlzheimerReport2015.pdf. Accessed June 14, 2017. 2. Wu YT,