Recruiting hard-to-reach populations via respondent driven sampling for mobile phone surveys in Colombia: a qualitative study oleh Camila Solorzano-Barrera, Mariana Rodriguez-Patarroyo, Angélica Tórres-Quintero, Deivis Nicolas Guzman-Tordecilla, Aixa Natalia Franco-Rodriguez, Vidhi Maniar, Prakriti Shrestha, Andrés I. Vecino-Ortiz, George W. Pariyo, Dustin G. Gibson, Joseph Ali