The 1940 Census Instructions provided enumerators with advice about who in the household to ask for information:
In order to obtain accurate and complete information, interview a responsible adult member of the household. Young children will usually be unable to give you the information desired for the Population schedule. Only occasionally will boarding or lodginghouse keepers be able to give you complete information concerning roomers or lodgers, and it is desirable, therefore, that, as far as possible, you obtain information directly from roomers and lodgers. Likewise, boarders, lodgers, and servants will seldom be able to give information concerning members of the household other than themselves. Obtain information about a household or a person from neighbors or other nonrelated persons only when it is impossible, after the second or third visit, to obtain the information through direct interview with a member of the household.
Bureau of the Census, “Instructions to Enumerators: Population and Agriculture” (1940), pp. 31–32.
According to the Instructions: Census workers should speak with multiple informants if lodgers or servants lived in the household. A lodger or live-in servant might not know very much about the family with whom they lived. Likewise, family members might not know very much about their lodgers or servants.
Instructions on “What to do when the census taker comes” in Benton and Bowles, Inc., Advertising Campaign for the 1950 United States Census, 1950. (National Archives)
Situation: In 1940, many (future) WWII Service members were still young adults living with their parents. Some, however, might be living in somebody else’s household. Imagine we are researching a WWII Veteran who was a lodger or servant in 1940. However, the census worker did not speak directly to them.
What should we do? In this case, we should treat the information with some caution. For example, we might guess that the Veteran’s age could be off by a few years.
First Lieutenant Leroi Shelton Williams, ca. 1943. (The Gilder Lehrman Institute of American History, GLC09587.116)
We have previously looked at WWII Veteran Mildred Aaberg in the 1940 census.
1940 US Census Population Schedule for Washington, DC. Enumeration District 1-295, Sheet 15B.