Values and mannerisms are difficult to pinpoint for a group encompassing millions of persons. Naturally, any large group of people will feature social diversity to some extent. However, some generalizations can be made using education and income as class defining criteria. William Thompson and Joseph Hickey noted that upper middle class individuals have a more direct and confident manner of speech. In her 1989 publication "Effects of Social Class and Interactive Setting on Maternal Speech", Erica Hoff-Ginsberg found that among her surveyed subjects, "upper-middle class mothers talked more per unit of time and sustained longer interactions with children". She also found that the speech of upper middle-class mothers differs "in its functional, discourse, and lexico-syntactic properties", from those in the working class.