According to Census 2000, 48.9 million people 5  years  old  and  over  living  in  housing  units  had  a   disability. 2    This   represents   19.2   percent   of   that    population.  The  Census  2000  Supplementary  Survey   (C2SS),  a  national  sample  that  used  the  American   Community   Survey   (ACS)    design,   estimated   that    39.7 million people aged 5 and over living in housing  units (15.6 percent) had a disability.   This  research  examines  elements  which  cause   the difference in the disability estimates between two  sources.  First,  this  research  examines  the  six  items  on   disability from the questionnaire which are combined  to  create  the  overall  disability  rate.  This  step  reveals   that   the   magnitude   of   di fference   in   employment    disability  rates  between  the  two  surveys,  C2SS  and   Census  2000,  is  greater  than  the  differences  in  the   other five disability items.   In  the  next  stage  of  analysis,  the  six  disability   items  are  compared  by  the  mode  of  data  collection.   Results  indicate  similarities  in  the  rates  at  which   some specific types of disability are reported by mail  respondents  in  both  surveys.  They  show  that  for  two   types of disability—difficulty going outside the home  to   shop   or   visit   a   doctor’s   office   and   difficulty    working  at  a  job  or  business—the  larger  differences   between the estimates of the two surveys occur in the  people counted in nonresponse follow-up operations.