Identifying Non-Working Numbers in Cell Phone RDD Samples via HRL-Lookup Technology

Abstract

RDD cell phone samples contain a substantial proportion of non-working numbers, making cell phone surveys relatively expensive. We tested a technology which allows users to automatically identify non-working numbers in a sample (Home Location Register Lookup or short HLR-Lookup). HLRLookup is available virtually in all countries where the GSM-standard is used – in about 200 countries (1). Though the GSM-standard coexists with other standards in many countries, it is estimated that about 80% of cell phone subscribers use it (2). The results presented here are especially useful for conducting surveys in European countries, since in Europe the GSM-standard is used exclusively, as well as in world regions where GSM tends to dominate other standards (Africa, Americas, Asia Pacific, and Middle East). Our findings will be of limited use for the US, since to our knowledge the proportion of GSM-subscribers in the US is not as high as in other countries (3) and technological standards used in the US are incompatible with each other, which does not allow screening of all sampled numbers via HLR-Lookup. In the meantime while the evolving technology may become more compatible in the future, the possibility of using HLR-Lookup to screen cell-phone samples and check numbers which belong to operators of the GSM-network should be considered by survey researchers in the US.