<prompt> Translate the following text to EnglishTofauti ndogo katika wingi wa posta ya Marekani ni kwa sababu ya tofauti katika ubora wa huduma ya utoaji ambayo hupunguza athari ya unene wa idadi ya watu kwenye njia nyingi.  <response>: 13 The smaller variation in U.S. postal densities is due to differences in the quality of delivery service which dampen the impact of low population density on many routes. 