I have personally scored more than 15 points differently at different times in my life.

The weight some people give to IQ is absurd. Psychometrics as a whole suffers a perpetual replication crisis.

+/- 7 on a scale from 50 to 150+ using different tests at different periods is very stable. It’s kind of shocking how little stuff like lack of caffeine alters the results while people really do score widely differently.

Not that I think the score actually means much, but consistency isn’t the problem.

It would perhaps be a more meaningful test of intelligence if a person took it 100 times over a few years. This, however, is not very realistic.

With 100 tests, the results would likely be skewed by the training …

IQ is the most solid and well-replicated part of psychometrics and psychology in general. It doesn't belong in the same category as growth mindset and power pose and other pop psychology.

It is, it just isn’t what most people think it is, nor was it ever meant to be.

You might be right, but I'm not quite sure what most people think it is, so I don't know.

It is not intended as a measure of giftedness. It is intended to measure proper cognitive functioning. In pop culture it is often talked about as a measure of genius.

I think it is a legitimate measure of giftedness at the top end. Genius, not so much.

Having an IQ of, say, 160 means you're extraordinarily capable of a broad range of cognitive tasks. It's more than merely proper cognitive functioning. But it doesn't mean you will be a world-altering genius. There are many stories of people with staggering IQs who ended up doing nothing notable, or producing a lot of interesting and odd ideas that ultimately had no impact on the world.

IQ is great on a population level, when administered by people who know what they are doing. On an individual level, especially when administered by a non-expert (or worse, online), it just doesn't offer as much information as living life does. As in, if I know I'm not an idiot, it's more likely my IQ test is wrong than that I'm wrong.

I also feel that there would be a likely Time-of-Day difference in test results.

For example (although only indirectly related), I can do Sudoku puzzles really well after I've been awake for a while. But for the first few hours of the day, I make lots of mistakes that I simply don't make once I'm fully awake and mobilized for the day.

Since it is such a bad test, what test do you recommend to replace it?

I think it is an excellent tool for what psychologists use it for.

So it can identify disabilities, but not abilities?