Within that constituency, interviewers were then told to find people with a given set of characteristics--ie, a certain proportion of men and women, of blue-collar and white-collar workers.

ECONOMIST: Why the polls got it wrong last time

Of course, if the samples are to be representative, interviewers need to contact the same proportion of, say, blue-and white-collar workers as there are in the population as a whole.

ECONOMIST: Why the polls got it wrong last time

The growth in real earnings for blue-collar professions--industry, warehousing and construction--have generally lagged those of white-collar workers.

FORBES: New Geographer

The same forces--technology and globalism--that quelled the wage growth of blue-collar workers may do the same to white-collar workers.

FORBES: Is College Worth It?

Unlike the manufacturing industry in the West that gave birth to a middle class of both white-collar and blue-collar workers, manufacturers in China mostly absorb surplus labor from rural areas with few skills.

FORBES: The Myth Of China's Manufacturing Power