Using a back-tested paper portfolio and an actual case, the authors of a study published in the Journal of Marketing found that companies at the top 20% of the the American Customer Satisfaction Index (ACSI) greatly outperformed the the stock market, generating a 40% return.

From 1996-2003, the portfolio outperformed the Dow Jones Industrial Average by 93%, the S&P 500 by 201%, and NASDAQ by 335%.

Past performance doesn't indicate future results. ACSI only goes back to 1994. However, these startling findings help vindicate one of our central claims: investing in customer service and satisfaction is good for your bottom line.