A researcher wants to examine the relationship between social class and number of books
read in a year. The first hundred people are interviewed as they enter a public library in the
researcher’s home town. On the basis of the answers given, the sample is categorized in
terms of a fourfold classification of social class: upper middle class/lower middle class/ upper
working class/ lower working class. Using Pearson’s r, the level of correlation is found to be
0.73 which is significant at p < 0.001. The researcher concludes that the findings have
considerable validity, especially since 73 per cent of the variance in number of books read is
