Efficiency vs. Effectiveness
I've heard before about the difference between efficiency and effectiveness, but today I thought of a particularly clear example: snow removal.
In Montreal, snow removal is effective. The moment it starts snowing, snowplows emerge all over the city, keeping roads and (especially) sidewalks clean as fast as possible. Considering how much snow we get, it's actually quite an impressive achievement.
In London, Ontario, snow removal is efficient. I rarely see a snowplow while it's still snowing; instead, they all come out at the end of the storm, do a single sweep, and they're done. This saves a lot of hours of work (and therefore taxpayer dollars) for the actual snow removal workers.
Which one is better? Well, think of it this way: if I'm trying to drive/walk somewhere, I don't much care how efficient the government of London, Ontario is at removing snow, because the streets and sidewalks are nearly impassable. But Montreal's effective snow removal gets me where I'm going, and makes me happy. (It might also be better for the economy, since you're optimizing global efficiency at the cost of a few snow removal workers.)
Efficiency is frequently used to rationalize ineffectiveness.
Next time someone wants to tell you how "efficient" a government programme or service provider is, ask them how effective it is and see if they even know what you're talking about.
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