1) E.g. Average number of household seems accurate to estimate number of cars sold in the US in one year or for number of light bulbs because you look at it from a household perspective. What about number of laptop or smartphones? In my opinion, I would use a view per person here and say for example that every person has a smartphone except childern and maybe elderly people (depending also on the country).

2) In the two videos about the replacement concept (cars and light bulbs): are we accurate when estimation the total number of existing light bulbs/cars by only considering households. There is also rental cars, business cars, taxis etc. which we don't include? Same for light bulbs: what about restaurants, hotels, offices etc.

Thanks for your help. Really appreciated

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