But research by Dutch economist Bart J. Bronnenberg and three colleagues from the University of Chicago makes you wonder why so many of us find the choice difficult. They used purchase data from more than 77 million shopping trips in America between 2004 and 2011 to find out what very well informed shoppers do when choosing between home brands and big brands. So which headache remedies do pharmacists chose and what pantry staples do professional chefs buy for their own kitchens?

It turns out that for a range of products well-informed shoppers favoured home brands. Pharmacists purchased home brand headache pills 92.5 per cent of the time – way above the American average of 74 per cent. In fact, households whose primary shopper was a healthcare professional bought far more store brands overall than others with a similar income. Professional chefs were much more likely to buy home brand food staples like salt, sugar and baking powder than non-chefs who were otherwise demographically identical.

"Across a range of products we find strong evidence that more informed shoppers buy more store brands and fewer national brands," Bronnenberg, Jean-Pierre Dube, Matthew Gentzkow and Jesse M. Shapiro conclude in their paper called "Do pharmacists buy Bayer? Informed shoppers and the brand premium" published by the National Bureau of Economic Research.

The study suggests the success of some big, national brands is largely the result of ignorance. It also underscores how much consumers waste because of uninformed choices. Bronnenberg and his colleagues estimate that American shoppers would save about US$44 billion a year if they switched to the store brand whenever possible.

Economists have identified many examples where the market behaviour of experts can be helpful to non-expert consumers. Research by University of Chicago economists Steven Levitt and Chad Syverson found real estate agents have an incentive to encourage their clients to sell their house as soon as possible. Because they receive only a small share of the incremental profit when a house sells for a higher value "there is an incentive for them to convince their clients to sell their houses too cheaply and too quickly. But when agents sell their own houses they are prepared to wait for the best price. Levitt and Syverson discovered agents left their houses on the market about 10 days longer than the typical vendor and received nearly 4 per cent more for their houses on average, even after controlling for a wide range of housing characteristics. Another example was revealed when economists Erin M. Johnson and Marit Rehavi examined how doctors gave birth. They found physicians were almost 10 per cent less likely to receive a caesarean section. "Financial incentives have a large effect on C-section probabilities for non-physicians, but physician-patients are relatively unaffected," they concluded. "Physicians also have better health outcomes, suggesting overuse of C-sections adversely impacts patient health."

But the expert shoppers Bronnenberg and his colleagues tracked were not always consistent. When it came to salt, sugar and baking powder health professionals purchases a similar proportion of big brand products as the rest of the population, despite their overall preference for home brands. While chefs were more likely than the average shopper to choose home brand pain killers they didn't buy them nearly as much as health care professionals.

Those with a tertiary qualification were more likely to buy home brands the average shopper. But the less-well educated were particularly prone to paying up for well-known brands. Sadly, many of them have little money to waste.