Des Moines-based Wellmark Blue Cross and Blue Shield and Principal Financial Group are among the best employers to work for in the country, according to an annual ranking by Forbes. Wellmark was ranked No. 3 on the list of 500 midsized companies, and Principal was ranked No. 4 among 500 large employers. The University of Iowa also appeared on the midsized employers list at No. 42 and University of Iowa Hospitals and Clinics ranked No. 48 in the large employer category. To determine the list, Forbes partnered with market research firm Statista to survey 30,000 Americans working for businesses with at least 1,000 employees. The respondents were asked to anonymously rate, on a scale of zero to 10, how likely they’d be to recommend their employer to others. Statista then asked respondents to nominate organizations in industries outside their own. The final list ranks the 500 large and 500 midsize employers that received the most recommendations.