sol invictus
Philosopher
- Joined
- Oct 21, 2007
- Messages
- 8,613
I'm glad you agree because this is for the example that YOU posed where there are 10 QSO all with the same deltaz (0.25) Maybe I misunderstood but I believe you said the overall probability was 0.5. That's wrong. It's 0.001, as I showed.
What I said (perhaps not perfectly clearly) is that for a typical random distribution, the probability for that distribution should be around .5 (by definition of "typical"). A typical random distribution will have an average deltaz of .25. If you could plug that average into your formula, you'd get P~.001 (which I said). Of course the actual values of P will be lower, since the points with deltaz smaller than .25 will matter more. Therefore, P is not the probability you want.
It's not wrong to use different deltaz.
If what you want to calculate is the confidence with which you can reject null hypothesis given the data, it is wrong.
Isn't it a fact that the probability for each QSO, by itself, can be determined individually as 2*deltaz. Just like in the above 1 QSO example. Correct?
The probability that a given QSO drawn from a flat distribution will be within deltaz of some point is proportional to 2deltaz, yes.
And isn't it a fact that the placement of each QSO is independent of the placement of any other. They are independent phenomena ... under the assumptions of mainstream theory. And given that the placement of the QSOs are independent of one another, isn't the joint probability the product of the probabilities of the individual placements?
That computes the probability of a very specific type of data set (one with those particular deltaz values). That's not at all what you want.
Look - let's make it even simpler. Suppose there's only a single data point, drawn from a flat distribution, and it's (I don't know) .22370000. Now, what's the probability of finding that result? My god - it's zero!!! The odds of finding that value, precisely that value, are 0!! And if there is some uncertainty in the measurement, the odds are proportional to that uncertainty (which might be very very small). So should we therefore reject the theory that the data was drawn from a flat distribution? OF COURSE NOT.
So the result is inescapable, even when the deltaz of each QSO is different. It's just simple math. I'm not wrong in this case, sol. The formula is correct for 1 "quasi-Karlsson" value and 10 quasars each a different distance from that "quasi-Karlsson" value.
No, the result is totally wrong. Or to be a little more precise - the probability you are computing is the probability of finding a very specific data set - one with one point within deltaz1, another point within deltaz2, etc. But we don't care about that, because (if the null hypothesis is correct) there is nothing at all special about that data set.
It's just like my example above - ANY data set has zero probability!
The random number cases you cited resulted in small probabilities, but that's as one would expect when the probability for any given point being within that points deltax from the "quasi-Karlsson" value is < 1. From the set of calculations you did, it would appear that the average probability you will get in that case is around 10-6 to 10-7 from random samples ... assuming the distribution they are drawn from is uniform across the total range. But what probability would you get if the set of QSOs you observed were are all fairly close to the midpoint ... say within 0.1? Why 10-10. A thousand orders of magnitude less. So the real measure of whether the QSOs are inordinately close is how small the probability is to that average probability you get if you assume a random placement.
Yes, that's a very crude way of getting closer to the real procedure. But the point is, the way you've defined things P=10^-7 does NOT mean anything - it is perfectly consistent with the null hypothesis.
If time and time again, you get probabilities that are many, many orders of magnitude smaller than what you expect to get on average, that might be an indication of a problem in your assumptions about the distribution of z.
Agreed.
I've never suggested that the single sample probability in my calculations isn't going to be a small value even if the distribution from which the z come is really uniform and not quantized.
Yes you have - many times.
But it's hard to evaluate what that small probability means, one way or the other, with just that alone. What's important is the final probability accounting for the maximum possible number of cases there could be with r quasars or even better, the number of cases actually examined to find the observations you have that contain those r quasar low probabilities cases. If you multiply the single sample probability by the total number of cases that might possibly exist, and you still end up with probabilities much less than one, and you have found numerous such cases, then perhaps it is time to reevaluate your assumption about the distribution of z in the total interval. OK?
As I keep telling you, what you would have to do is compute what fraction of the possible data sets are MORE significant (more tightly clustered around the Karlsson values) than the one you actually measured. That fraction is something close to the real significance (for example, in the case above with 10 QSOs the typical P value was around 10^-7, so a P value like that is not at all significant, but a P value of 10^-10 would be).
You have done not done such a calculation, so the smallness of the P values you were finding is completely meaningless.
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