Maartje Boer

SMU AND WELLBEING ACROSS COUNTRIES 109 4 Country-Level Measures Country Prevalence Intense SMU The prevalence of intense SMU was calculated as each country’s proportion of respondents that were classified as intense users. Country Prevalence Problematic SMU The prevalence of problematic SMU was calculated as each country’s proportion of respondents that were classified as problematic users. Mobile Internet Access Two measures obtained from OECD-data were used (OECD, 2019). Costs of mobile broadband was assessed using the countries’ average price of a basket of mobile monthly usage of 300 calls and 1 gigabyte internet in 2017. To facilitate international comparisons, prices were standardized by taking into account different price levels between countries (OECD, 2019). Countries’ internet speed was indicated by download speed inmegabits per second in 2017. Analysis Missing Data In the analysis sample, 22.4% of respondents had missing data on at least one individual-level variable, with problematic SMU having the most missing data (9.8% of the analysis sample). To retain all respondents, missing data were imputed using multiple imputation with Mplus 8.3. Five imputations were generated using the default unrestricted ‘covariance’ method (Asparouhov & Muthén, 2010b). Missing data were imputed based on available data on the individual-level study variables as well as dummy variables indicating countries to account for the nested structure of the data (Reiter et al., 2006). Iceland did not have data on internet speed, and Lithuania did not have data on mobile broadband costs. To retain these countries, these two missing values were imputed based on available information on countries’ Gross Domestic Product (GDP), number of mobile broadband subscriptions, average data usage per mobile broadband subscription (OECD, 2019), and countries’ intense and problematic SMU prevalence.