A new study shows how a useful rule of thumb can become an expensive assumption when it starts deciding which customers deserve attention.

I’ve often referred to the 80/20 rule in marketing and business because it feels right.

A relatively small share of customers, decisions or effort often account for a disproportionate share of whatever outcome.

I’ve usually meant that as a broad observation, with zero expectation that somebody counted everything precisely.

Now a far-reaching new study gives that instinct some cred, along with a reason to watch where we go with it.

Researchers examined 16 years of U.S. household expenditure data, from 2009 through 2024.

Across 14 broad categories, weighted by their share of spending, the highest-spending 20% of buying households accounted for about 51% of expenditure.

Despite all that went on during those years, the overall pattern stayed amazingly stable.

The category differences were substantial: the top 20% accounted for 39% of food spending and 83% of education spending.

A fifth of buyers generating so much of the spending still gives us plenty of reason to pay attention to concentration.

It also leaves roughly half the spending with everybody else.

That’s a sizeable market to overlook because a memorable rule suggested the remainder was relatively unimportant.

The research concerns category spending, so it can’t tell us how revenue is distributed across your customers, or which marketing activities produce the best returns.

It certainly doesn’t make 50/20 into the new scientific law.

For the product marketing work I discuss in I Need That, the useful habit is to investigate those differences before building a strategy around them. Check your own customers’ contributions, including what it costs to serve them. Spending and profitability are different measurements.

I’ll keep using 80/20 to remind myself to look for uneven contributions.

But I’ll be more careful when the shorthand starts making budget decisions.

If you’d like help creating and marketing products people feel compelled to buy, the product marketing consultants at Graphos Product can help.