“…As other countries [ 10 , 11 , 12 , 13 , 14 ], Germany faces difficulties in adequately including hard-to-survey populations, amongst others people with migration history, people with lower educational levels, and people living in deprived areas, into nationwide public health monitoring. Several studies identifying ways on how to reach hard-to-survey populations either focus on specific sub-populations [ 15 , 16 , 17 , 18 ] and areas [ 16 , 19 , 20 ] or on inclusion into specific study types, for example, clinical trials [ 21 ] or intervention studies [ 15 , 22 ]. Recommendations on how to include hard-to-survey populations into a comprehensive public health monitoring are scarce [ 23 , 24 , 25 ].…”