I Advantage of having more measurements

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  • #51
Ah, sorry this was my mistake. I forgot B had some experimental uncertainty in our discussion. To be honest, when ##B## depends on the measured quantities, I'm less confident in my claim. However, in equation 11 of the Solaro paper, it looks like "B" doesn't depend on any measured quantities. Am I missing something?
 
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  • #52
Twigg said:
Ah, sorry this was my mistake. I forgot B had some experimental uncertainty in our discussion. To be honest, when ##B## depends on the measured quantities, I'm less confident in my claim. However, in equation 11 of the Solaro paper, it looks like "B" doesn't depend on any measured quantities. Am I missing something?
My bad! Seems like in general that can be factorized as ##A/(BC)##, where A and C are experimental parts and B is only theory. But my other questions still remains. In this case why do we care about ##BC## at all? What we measure in practice is A and that is what tells us if we made a discovery or not so it seems like the ##BC## term just adds a lot of complications, without telling us anything about whether we found something or not.
 
  • #53
I think it's just cosmetic, and to make the result easier to communicate. From a measurement / statistics standpoint, the theoretical "B" coefficient does not matter. However, if you had two groups doing isotope shift measurements, one doing measurements in Ca and one doing measurements in radium or some fancy stuff, they'd need a quantity that was species-independent to compare results. That's where B comes in. Also, I think tying the experimental quantities to theory is just something that journals expect from authors.
 
  • #54
Twigg said:
I think it's just cosmetic, and to make the result easier to communicate. From a measurement / statistics standpoint, the theoretical "B" coefficient does not matter. However, if you had two groups doing isotope shift measurements, one doing measurements in Ca and one doing measurements in radium or some fancy stuff, they'd need a quantity that was species-independent to compare results. That's where B comes in. Also, I think tying the experimental quantities to theory is just something that journals expect from authors.
Sorry, my questions was not very clear. I was actually more curios about the C term. When doing error propagation we need to propagate the error from C, too, as it is an experimental term. However the discovery potential of the measurement is contained in A, in terms of the measured quantities. Why do we need to propagate the error from C, too and not just treat is as B?
 
  • #55
It's not clear to me off the bat how to interpret the final result "##y_e y_n##", but I'm guessing it's significant and has something to do with the intermediary bosons, but the beyond-standard-model theory aspect of this is way, way over my head. You might attract the attention of smarter folks than me by posting a new thread about the new physics behind this measurement. Sorry I couldn't be more help
 
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  • #56
Twigg said:
It's not clear to me off the bat how to interpret the final result "##y_e y_n##", but I'm guessing it's significant and has something to do with the intermediary bosons, but the beyond-standard-model theory aspect of this is way, way over my head. You might attract the attention of smarter folks than me by posting a new thread about the new physics behind this measurement. Sorry I couldn't be more help
You helped me a lot! I understood a lot about the approaches to this kind of experiments from your replies. Thank you so much!
 
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  • #57
kelly0303 said:
Hello! I have some points in the plane, with errors on both x and y coordinates. The goal of the experiment is to check if the points are consistent with a straight line or not i.e. if they can be described by a function of the form ##y = f(x)=a+bx## or if there is some nonlinearity involved (e.g. ##y = f(x)=a+bx+cx^2##). Assume first we have only 3 points measured. In this case, the approach is to calculate the area of the triangle formed and the associated error, so we get something of the form ##A\pm dA##. If ##dA>A##, then we are consistent with non-linearity and we can set a constraint (to some given confidence level) on the magnitude of a possible non-linearity (e.g. ##c<c_0##). If we have 4 points, we can do something similar and we can for example calculate the area of the triangle formed by the first 3 points (in order of the x coordinate), ##A_1\pm dA_1## and the area of the last 3 points ##A_2\pm dA_2## and then sum them add and do error propagation to get ##A\pm dA## then proceed as above (in the case of this experiment we expect to not see a non-linearity so we just aim for upper bounds). My question is, what is the advantage of having more points? Intuitively, I expect that the more points you have, the more information you gain and hence the better you can constrain the non-linearity. But it seems like the error gets bigger and bigger, simply because we have more points and error propagation (you can assume that the errors on x and y are the same, or at least very similar for different measurements). So, assuming the points are actually on the line, for 3 points we get ##0\pm dA_3## and for, say 10 points we get ##0\pm dA_{10}## with ##dA_{10}>dA_3##, so the upper bounds we can set on the non-linearity are better (smaller) in the case of 3 points. But intuitively that doesn't make sense. Can someone help me understand what I am doing wrong. Why is it better to have more points? Thank you!

This may already be covered, I haven't read the entire thread, sorry.
I'm a retired cartographer/analyst programmer working for NSW (Australia) state mapping and geodetic survey authority. The advantage of more points is to determine precision. Precision is not accuracy it is consistency. You can for example express precision as a standard deviation, usually 90% of a sample is within 3 standard deviations and this is the usual way to express precision. I don't like the concept of basing straightness on the area of a triangle because the further points are apart, the larger the area even though the precision is the same. I think you would be better off using linear regression which is a statistical approach and will give you the mean line through the points as well as a correlation coefficient expressing how well the points fit the mean line through them. This can be done in Excel. In fact, you can even do curve regression in Excel and it will give you an expression for the curve which is really handy for trend and relationship analysts. Hope that makes sense.
 

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