Study title

+++++++++++++++ Version 1.0.0 of the study is outdated and therefore not available any longer . Please use the revised version 2.0.0 here . +++++++++++++++ Institutionalization, cognitive impairment and inability to conduct an interview due to health impairment are among the top exclusion criteria for most large-scale social and aging surveys. Reservation against targeting vulnerable groups results from economic or legal restrictions of recruitment and concerns about research ethics or the validity of data obtained. However, failure to include those individuals may lead to substantial bias. Metadata showed that privileged data access and checks against nursing home repositories prevented under-coverage of the institutionalized. Measures to include hard-to-survey groups led to a marked increase in response rate. Individuals with health impairment contributed substantially to representativity of the sample. Nonresponse bias was cut to half compared to a less inclusive study protocol. Judged from a total-survey-error perspective, reductions in nonresponse-bias, low item-nonresponse and evidence of measurement invariance across self- and proxy-report for key characteristics suggest significant benefits of including hard-to-survey groups in estimating characteristics of this population.