15. Lessors of Miniwarehouses and Self-Storage Units: 11%
16. Insurance Agencies and Brokerages: 11%
17. Other Activities Related To Credit Intermediation: 10.7%
18. Investment Advice: 10.7%
19. Offices of Physical, Occupational and Speech Therapists, and Audiologists: 10.6%
20. Offices of Physicians (except Mental Health Specialists): 10.4%
Thirteen of the top 20 categories involve professional services that require years of training and certification, from healing the sick to balancing financial accounts. Three big perks with professional services: consistent demand, relatively low overhead and what economists call "high switching costs." (If someone's been doing your taxes for 20 years, why would you switch?) Little surprise that manufacturing and retail–industries with few economies of scale–didn't make the cut.
Size matters too, even within the small-company universe. Tiny shops may not require a lot of overhead, but at some point–say, a few million dollars in revenue–the relative level of overhead spikes, crimping margins.
To be fair, these numbers are something of a snapshot, as the profitability of a given industry ebbs and flows with the overall economy. (Some industries get permanently disrupted along the way–just ask those of us in the publishing business.) Another thing to remember about profit margins: A business can appear very profitable on a percentage basis but not generate great piles of money–especially if the principals are pulling out every last dollar to cover private-school tuition fees and summer-home mortgages.
