You can tell this is a poll of what people perceive to be the important jobs because doctor is #1. The most important jobs by sector in order of importance for developed nations is
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power supply- we all need electricity and few of us have the ability to generate it ourselves
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water supply- getting enough clean water for your day to cook and wash is a near full time job. For Americans a gallon of water is roughly 8lbs and your average toilet uses 3-5 gallons per flush. It would take much of the day to get and purify the water you use
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sanitation workers- this the poll got right. The folks collecting waste do more directly for public health than most doctors could hope to do.