My great uncle was Alexander Gillis was born Parish of Harris in Dec 1840. He married as his second wife Christy Shaw a widow. I find them in various records and Census but very inconsistently in the Census. 1. 1841 Scottish Census Age 64 months, born Dec 1840 2. 1871 Census Alex widower with 3 children and Christy Shaw widow and housekeeper in Lingan 3. 1874 Alex and Christy marry 4. 1875 Daughter Florence born. 5. 1880 US Census, not found (searched but not unexpected) 6. 1881 Census (family search) A, C and F not found. 7. 1891 Census. Not found 8. 1896 Florence married, dau of Alexander in mining and Christy 9. 1901 Alexander and Christy living in Glace Bay 10. 1908 - 1911 No death found for Alexander or Christy 11. 1911 Neither found Does anyone have estimates on what percentage of persons were missed in the various Census?