Nairobi, May 5 -- My wife had a hearty laugh on my account when I showed up with a fancy-looking cough syrup a couple of evenings ago. They have sold you the most expensive kind, she said, in amusement.

Suffering a slight dry cough at the end of a bout of flu, I popped into a chemist on my way home. May I have cough syrup please, I asked the young man behind the computer on a counter.

What kind of cough is it, he inquired? Dry, I said. How long? A couple of days, I reported. When is it worst, morning or evening, he quizzed, concern in his voice? Mmmm, morning I said, hesitation evident. He gave me a propolis-based syrup.

My wife's mirth got us talking about price discrimination, a strategy where businesses charge different prices to di...