What could be the likely reason that my ancestors did not appear on the 1891 and 1901 census?

Question

What could be the likely reason that my ancestors did not appear on the 1891 and 1901 census?

Answer 1

They were either abroad, in jail, or just avoiding the tax man

Answer 2

I think the census is done in the even 10 year, 1890 and 1900.

Answer 3

Lets see.

(a) they emigrated or were abroad somewhere.  

(b) they died before these dates

(c) they are there but mistranscribed in the online indexes under a different spelling or name.  This is probably the most likely.

(d) the district in which they lived have pages missing and aren't in the indexes.  For example, most of the Dunmow district in Essex is completely missing from the 1851 census as are huge parts of Manchester.  

(e) they were missed off the census by the enumerator - either deliberately trying to avoid him or by accident.  They might not have been home on census night and been missed off.  Certain sections of society like gypsies or travellers would have been missed off the census anyway.  In certain cities like London, then as now, there were some inner city areas in which the enumerator feared to tread.  They were only volunteers doing their best, and wouldn't want to hang around in the wrong part of town asking questions of people who didn't really want to answer them!

(f) They could have been in prison - not all prisoners were refered to by name, some simply by their initials.  

(g) If they were serving abroad in the army or other armed forces then they would probably have been missed off the census too.

Answer 4

They did not live in England (assuming it's an English census) at the time

They had changed their names

They were living somewhere illegally and didn't want to give their names to the census takers

They had some other reason for not giving their names

The census taker didn't record their names

Answer 5

They might not have been in on the night, the census taker might have misreported their names for example 2 of Tunnicliffe ancestors are recorded as Sunnicliffe.