I have a series of data coming from an instrument, (e.g. spectrophotometer), let’s say 10 wavelenghts and 5 repetitions of the measure.
matrix X (xij) i=1,10 (wavelenghts) j=1,5 (measures) I want to calculate the “mean total signal” with its uncertainity. Choice 1) I calculte the mean value of the signal for each of the 10 wavelenghts (xi mean, mean value over j) with its standard deviation. I calculate the mean total signal as a sum (over i) and its relative uncertainity as the square root of the sum of the squared relative uncertainities Choice 2) I calculate the sum of the 10 signals for each of the 5 repetitions (sum over i) I calculte the mean value (over j) and the standard deviation for these sums Results are (obviously) different. What’s the correct procedure? And most of all, why? Thanks in advance References are welcome. rob ex:data 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 choice1 21 22 23 24 25 26 27 28 29 30 mean=255 choice2 55 155 255 355 455 mean=1275 . . ================================================================= Instructions for joining and leaving this list, remarks about the problem of INAPPROPRIATE MESSAGES, and archives are available at: . http://jse.stat.ncsu.edu/ . =================================================================
