Census Takers / Enumerators
Many enumerators were not well qualified.
Some enumerators did not follow instruction (i.e. initials only, no birth places listed, etc.)
Some enumerators used unfamiliar abbreviations and ditto marks (i.e. Conn., Ct., Cn., Cnct. were all used for Connecticut).
Instructions were not given about the physical path a census taker should follow when gathering the census information, only that he must cover the entire territory assigned to him. People who live on adjoining property might be listed several pages apart, depending on the route taken by the enumerator.
Emumerator may have missed a page by turning two pages at a time and by returning to the missed page the dwelling numbers or family numbers were recorded out of sequence on the pages.
Incorrect information was sometimes given by family members, memory might be poor (most people did not read or write)
Incorrect information was sometimes given due to lack of understanding the question.
If adults were not home, sometimes answers were requested of small children or neighbors or the enumerator guessed the answers himself.
Families were sometimes left off the census because they were away visiting relatives.
Some families lived in multi-dwelling units or remote country dwellings and were overlooked.
Some families were missed, due to the length of time it took to take the census.
Poor quality paper and ink
Difficulty in reading microfilm copies (due to poor photography, double papers or pages filmed, making writing too small, etc.).
Also filmer might miss a page by accidentally turning 2 pages.