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Old 19th April 2017, 05:51 AM   #241
3point14
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Is an EM drive being tested aboard an X37B?

I'm guessing not.

https://www.sciencealert.com/rumours...just-won-t-die
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Old 19th April 2017, 11:46 AM   #242
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Originally Posted by 3point14 View Post
Is an EM drive being tested aboard an X37B?

I'm guessing not.

https://www.sciencealert.com/rumours...just-won-t-die
Quote:
The EM Drive is a little like the Kardashian of the science world - it hasn't been proven to actually do anything as yet, but, still, we can't stop reading about it.
:-)
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Old 21st April 2017, 12:16 AM   #243
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Originally Posted by Beelzebuddy View Post
The relationship may not be as linear as the authors would like, but that's not the same thing as there not being a relationship.
Figure 9 shows 60W produced more thrust than 40W or 80W. You'd expect this kind of numbers if the thing didn't work and the observed thrust was a source of hitherto unknown error in measurements.

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Old 23rd April 2017, 06:29 PM   #244
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Originally Posted by McHrozni View Post
Figure 9 shows 60W produced more thrust than 40W or 80W. You'd expect this kind of numbers if the thing didn't work and the observed thrust was a source of hitherto unknown error in measurements.

McHrozni
Figure 9 has crap for confidence intervals. Other than "it probably gets bigger," there is literally nothing we or the authors can say about it.
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Old 24th April 2017, 03:27 AM   #245
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Originally Posted by Beelzebuddy View Post
Figure 9 has crap for confidence intervals. Other than "it probably gets bigger," there is literally nothing we or the authors can say about it.
Hm, it says the thrust at 40W is 30 6μN and rises to 106 6 μN at 60W, but drops back to 76 6μN at 80W.

As stated there would be more thrust at 60W than at 40W. The fact there is less thrust at 80W than at 60W leads me to believe their confidence intervals are bollocks, but the authors stated there was a measurable and statistically meaningful increase in thrust. Or am I missing something?

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Old 24th April 2017, 04:19 AM   #246
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Originally Posted by McHrozni View Post
Hm, it says the thrust at 40W is 30 6μN and rises to 106 6 μN at 60W, but drops back to 76 6μN at 80W.

As stated there would be more thrust at 60W than at 40W. The fact there is less thrust at 80W than at 60W leads me to believe their confidence intervals are bollocks, but the authors stated there was a measurable and statistically meaningful increase in thrust. Or am I missing something?

McHrozni
The instrument error is 6 uN*. The measurements produced by that instrument are all over the place. That is what gets factored into confidence intervals. Those should be the purple whiskers behind each grouping, although those don't appear to be confidence intervals either - a quick back of the envelope says the SEM of the 60W group should be +- 23 uN, not the fifty-something they label.

*Almost certainly determined using optimal conditions, and not something on the bare edge of detection.
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Old 24th April 2017, 04:34 AM   #247
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Originally Posted by Beelzebuddy View Post
The instrument error is 6 uN*. The measurements produced by that instrument are all over the place. That is what gets factored into confidence intervals. Those should be the purple whiskers behind each grouping, although those don't appear to be confidence intervals either - a quick back of the envelope says the SEM of the 60W group should be +- 23 uN, not the fifty-something they label.

*Almost certainly determined using optimal conditions, and not something on the bare edge of detection.
Yeah OK, that's a bit different.

Still, 106 23μN is larger than 30 23μN. The true uncertainty would have to be about 38μN for the two results to be statistically indistinguishable. My take is that it is indeed either indeed this large or that the large measurement at 60W is bogus in some other way.

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Old 24th April 2017, 10:17 AM   #248
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Originally Posted by McHrozni View Post
Yeah OK, that's a bit different.

Still, 106 23μN is larger than 30 23μN. The true uncertainty would have to be about 38μN for the two results to be statistically indistinguishable. My take is that it is indeed either indeed this large or that the large measurement at 60W is bogus in some other way.

McHrozni
That's still not quite right. 23 uN is the confidence interval around the average of their 60W measurements, not something applied to each of the measurements or the other wattages.

To use an analogy, have you ever noticed that when you take your temperature multiple times in a row, you'll get slightly different numbers each time? That happens because of a lot of factors - instrument error, how you're holding it, where you're holding it, etc, but each measurement is helping create a sample of your unknown true temperature. Do it a couple of times and you can start averaging the measurements together and using their spread to predict how accurate the mean probably is, mathematically known as the Standard Error of the Mean. A little less than double that will get you a 95% confidence window in which your true temperature most likely falls.

I worked up the 40W measurements here.
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Old 24th April 2017, 10:53 PM   #249
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Originally Posted by Beelzebuddy View Post
That's still not quite right. 23 uN is the confidence interval around the average of their 60W measurements, not something applied to each of the measurements or the other wattages.
I was under the impression that 106μN and 30μN were average measurements at 60W and 40W, respectively.
Alas, it is true my knowledge of statistics is limited and I acknowledge it needs to be updated

Can you maybe point out a good online tool to study it a bit? It would be useful for my work. Thanks

McHrozni
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Old 25th April 2017, 10:31 AM   #250
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Originally Posted by McHrozni View Post
I was under the impression that 106μN and 30μN were average measurements at 60W and 40W, respectively.
Alas, it is true my knowledge of statistics is limited and I acknowledge it needs to be updated

Can you maybe point out a good online tool to study it a bit? It would be useful for my work. Thanks

McHrozni
Frankly, the best place to start is wikipedia. Its only problem is it sometimes trips over itself trying to present inscrutable mathematical derivations rather than anything which can be reasonably scrut.

Have a look at their standard error page. It has the formulas I used in the code above. Do you need more or less rigorous math than that?
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Old 25th April 2017, 10:57 AM   #251
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Originally Posted by Beelzebuddy View Post
Frankly, the best place to start is wikipedia. Its only problem is it sometimes trips over itself trying to present inscrutable mathematical derivations rather than anything which can be reasonably scrut.
I don't know if this helps with that, but there is the Simple English edition of Wikipedia. Here is their page on standard error.
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Old 25th April 2017, 01:55 PM   #252
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Originally Posted by McHrozni View Post
I was under the impression that 106μN and 30μN were average measurements at 60W and 40W, respectively.
Alas, it is true my knowledge of statistics is limited and I acknowledge it needs to be updated

Can you maybe point out a good online tool to study it a bit? It would be useful for my work. Thanks

McHrozni
Not an online tool, but I like the NIST Sematech e-handbook of statistical techniques. I'm on a phone so posting links is a pain but it's worth a Google.

It pretty much describes my approach to exploratory data analysis, which works very well in my sorts of engineering. Basically plot the data in lots of different ways before guessing what statistical tests to perform.
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Old 25th April 2017, 10:51 PM   #253
McHrozni
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Originally Posted by jimbob View Post
Not an online tool, but I like the NIST Sematech e-handbook of statistical techniques. I'm on a phone so posting links is a pain but it's worth a Google.
Can you just confirm if this is it?

http://www.itl.nist.gov/div898/handbook/

Thanks

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Old 25th April 2017, 10:52 PM   #254
McHrozni
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Originally Posted by Beelzebuddy View Post
Frankly, the best place to start is wikipedia. Its only problem is it sometimes trips over itself trying to present inscrutable mathematical derivations rather than anything which can be reasonably scrut.

Have a look at their standard error page. It has the formulas I used in the code above. Do you need more or less rigorous math than that?
Wikipedia is useful for looking something up, I need an explanation of when to use which tool, i.e. the reverse of what Wikipedia is good at.

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