Chronology Current Month Current Thread Current Date
[Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

[Phys-L] Re: For pot watchers: is it a conspiracy?



Yes it looks good. However, as one author wrote (paraphrased) those who
do Chi by eye deserve what they get.

So I tried Pearson's test w/ 42 intervals (single day) and m the claimed
0.274/day. I should have stopped there, as there are only three classes
(0, 1, & 2) should be at least 5. Anyway, I found Chi square = 0.52 w/
one deg. of freedom. Using the fig. in Evans (p.776) p= ~ 0.5 i.e.
good agreement w/ Poisson distrib. However, I did violate the condition.

So I tried three day intervals. This time the data looked bad!, and Chi
square = 13 w/ three degs. of freedom. p = ~ 0.01 rather unlikely
agreement w/ Poisson distrib. Requirement still not fulfilled, but more
nearly so.

So "went to" Leigh's reference for more data. Nope. Then I turned the
page in Evans and found "An Extension of the Chi-square Test" cutting
to the chase, only n need be > 5 (it's 42), and I obtained p ~ 0.2
Again a bit ambiguous as it should be between 0.3 and 0.4

Evidently I've gone wrong; where?


bc, not a statistician



Leigh Palmer wrote:

If you have never done this (below), you are a theoretician!

Have you ever sat and watched a counter register hits
supposedly occurring randomly in time, like a radiation
counter? That is, of course, a rhetorical question. Well, my
son David was doing just that for an agonizingly long time
while watching results come in from the Swift gamma ray burst
instrument, wondering why the instrument had quit working. I
enclose a snippet from the Swift Mission Director's Status
Report Log
http://swift.gsfc.nasa.gov/docs/swift/operations/status_log.html
to describe this seemingly non-Poissonian run of luck:

July 20, 2005

Swift has continued to amaze us with its record of burst
discoveries. We've learned first hand what 'random' truly
means. From June 7 to July 1, the BAT detected no new GRBs.
After July 1, we had no GRBs until July 12. Since July 12,
the BAT has found seven new bursts! So in these six weeks,
we've seen eight bursts [which is not too far from the
average rate of 100 per year] but almost all of them are
in the last week!

Swift is apparently working fine, so this lacuna is real. I
leave it as an exercise for the reader to calculate the *a
priori* odds on this observation. I suspect David did the
calculation several times, apprehensively, during the apparent
hiatus. He did share his concern with me during that time.

Leigh

_______________________________________________
Phys-L mailing list
Phys-L@electron.physics.buffalo.edu
https://www.physics.buffalo.edu/mailman/listinfo/phys-l