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What's the standard deviation of values in the histogram bar

  1. Nov 17, 2017 #1
    1. The problem statement, all variables and given/known data
    If one bar of a histogram has been generated with ##n## entries from a total of ##x## measurements, i.e. the event occurs randomly ##n## times in the ##x## event interval, then what is the standard deviation of values in this bar? Let ##k## be the range of values that could have been measured for this particular bar of the histogram, and assume that the expectation value of ##k## is ##n##.

    2. Relevant equations


    3. The attempt at a solution
    I'm finding the wording tricky to understand. ##n## is the number of events in the interval, and the average value of ##k## is also ##n##? The variance is the square of the distance from the mean and if all the events were equally likely, I'd divide by ##n## and have something like
    ##\frac{1}{n}\Sigma(k_i - n)^2##
    But I'm not sure that's what it means when it says the event occurs randomly a total of ##n## times. I'd really appreciate any hints on how to tackle this, thanks for any help!
     
  2. jcsd
  3. Nov 17, 2017 #2

    mfb

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    Staff: Mentor

    It is strange to define k as a range. The range should be 0 to x.

    I guess you have to assume that the x measurements are independent.
     
  4. Nov 17, 2017 #3
    Would you say then that ##k## is the class width of the single histogram bar being considered? That's how I've interpreted it. I also thought it would be quite a strange coincidence if the number of events ##n## recorded, which corresponds to the area of the bar, happened to be also the average value of ##k##. Which is what I take all the above to mean.

    I think the wording is very confusing, but I've written it as it was given to us.
     
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