Detailed interviews were conducted with over 1000 street vendors in the city of Puebla, mexico , in order to study the factors influencing vendors' incomes. (World development, Feb.1998) . vendors were defined as individuals working in the street , and included vendors with carts and stands on wheels and excluded beggars, drug dealers , and prostitutes. The researchers collected data on gender , age , hours worked per day , annual earnings , and education level. A subset of these data appears in the table.