I've heard variously that exhibit texts should be at the 5th grade/
6th grade/12-year-old level.

An article in the online "Economist" (http://www.economist.com/),
"Training and Jobs" cites a relevant survey by the OECD (?).

Men who "could not understand the instructions on an aspirin bottle:"
Sweden...1 in 12
Netherlands...1 in 10
Germany...1 in 7
US and Canada...1 in 5

Gender jokes aside, this suggests 20% of potential adult domestic
visitors are not going to comprehend a very high level of exhibit text, and
is in keeping with the frequently-cited estimate that 1 in 5 adults in the US
are not functionally literate in English.  Another reason why reliance on other
media besides text is so critical to understanding!

TV
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