In reality, of course, price discrimination is not perfect. Customers do not walk
into stores with signs displaying their willingness to pay. Instead, firms price discriminate
by dividing customers into groups: young versus old, weekday versus
weekend shoppers, Americans versus Australians, and so on. Unlike those in our
parable of Readalot Publishing, customers within each group differ in their willingness
to pay for the product, making perfect price discrimination impossible.
How does this imperfect price discrimination affect welfare? The analysis of
these pricing schemes is quite complicated, and it turns out that there is no general
answer to this question. Compared to the monopoly outcome with a single price,
imperfect price discrimination can raise, lower, or leave unchanged total surplus
in a market. The only certain conclusion is that price discrimination raises the monopoly’s
profit—otherwise the firm would choose to charge all customers the
same price.