I'd like to hear some alternatives. I personally prefer indexed scores, which can consider multiple variables at a time, which can tend to obscure the greater reality one might find in these countries.

That would take Canada off the list!
Pumping sewage out into the ocean is hardly 'proper and maintained'.

It may be too simplistic an answer but it has to have a proper and maintained sewage system.
Think it through, countries with exploding populations and no sewage system suffer from pollution, poor economies, unrest and disease. Those who have it have good economies, stable governments, and a middle class.
Theres likely a lot more to it, good education system as an example, but overall, it seems to be applicable.

I wouldn't say France is developed, considering it relies on other countries' money to stay rich.
Britain contributes billions each year to the Common Agricultural Policy, of which France is the main benificiary because its farmers, unlike those in Britain, are inefficient and lazy. And if Britain didn't have its EU rebate, which France wants to take off us, it would pay an incredible 14 times more to the CAP than France despite having a similar sized economy.
And France doesn't even spend its CAP money on actual agriculture, as that newspaper report from a few years ago which showed French farmers - who do nothing - posing by their sports cars paid for by the generous English (the Scots, Welsh and Northern Irish also only survive thanks to English money) taxpayer.
And the pitch in France's national football and rugby stadium, the Stade de France, is a disgrace. They can't even grow proper turf.
Well, to me, the main criteria is per capita income or per capita GDP. There are some other minor criteria (industrialization, Human development Index etc.), but per capita income is the major criteria.

I never said it was the sole criteria, Tenpenny. But it is at least the main criteria. And in the definition I have posted, it indeed was the sole criteria. So it can be the sole or the main criteria.

Quite so; it is but it isn't, and I said it was but I didn't say it was.
You're trying to argue about nothing, because I agree with you completely when you say that you said it or you didn't say it, and that it is or it isn't.
It's quite refreshing that you have opened your mind, and are now able to see the Truth.

I noticed this thread just now, and as I expected, it degenerated into trivialities, everybody saying why a particular country is not developed. The conclusion seems to be that no country in the world is developed. Then why do we talk of developed and developing countries?
Which really emphasizes the point I made in the other thread. Everybody is expressing their opinion as to which country is developed and which isn’t, without much concrete evidence.
Well, to me, the main criteria is per capita income or per capita GDP. There are some other minor criteria (industrialization, Human development Index etc.), but per capita income is the major criteria. You usually cannot have industrialization or high Human Development Index without also high per capita income or per capita GDP.
Anyway, I go by the International monetary Fund list of developed and developing countries. Anything else is pure speculation, personal opinion without any evidence.
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Anyway, here is one specific definition (there are other, less specific definitions).
In its most recent classification, economies are divided using 2008 Gross National Income per capita. In 2008, countries with GNI per capita below US$11,905 were considered developing.

And where did I say that that was the sole criteria? Mind you, according to one definition that is the sole criteria. So I wouldn't be wrong if I said that is the sole criteria. So you are arguing about nothing.
But what I am saying here is that a country cannot be developed without high per capita income, per capita income has everything to do with it. But other factors could also contribute.
But I fail to see how you go from one to the other.
Let me give you an analogy. Being intelligent, being smart has everything to do with becoming a doctor. That doesn't mean that that is the only factor. What that mean is that if you are not intelligent, you won't become a doctor.