Flashcards in L1 Craig: INTRODUCTION TO THE STATISTICAL ANALYSIS OF EXPERIMENTAL DATA Deck (25):
what should uncertainty be estimated and quoted as?
what does uncertainty determine?
precision of the measured result
If you now the true value what can you do ?
measure ether accuracy
what is absolute uncertainty?
actual magnitude of the uncertainty
what is relative uncertainty ?
expressed as a fraction or percentage of the measured value e.g. Dx/x or 100 x Dx/x %
should the uncertainty be quoted to the same level of precision as the measurement itself ?
what does it mean if no uncertainty is quoted?
last figure in the measurement is the best that can be determined
so uncertainty is half of this
what are the 2 categories of uncertainties ?
random and systematic
what's random uncertainty?
produces a scatter of values due to random effects such as poor resolution, electrical noise, human failings; for single measurement it must be estimated; for repeat measurements it may be calculated.
what is systematic uncertainty ?
arises through incorrect calibration or mistake in experimental design often resulting in an off-set value (bias); once identified it is often possible to correct for such an error.
why do we repeat measurements?
• Identify possible outliers–
• Calculate a mean
• Estimate the uncertainty
what are outliers?
values that appear way out of line and may be due to some one-off, gross error.
When only random errors are present the best-value is.....
average or mean
In practice often only a few (n < 12) repeat measurements are available. In this case the______ is a better estimate?
what is standard error?
property of a set of measurements
what is standard deviation?
a population of numerical data through a statistical distribution
what des standard error depend on?
number of repeat measurements
rank and its the middle value
most common value
why is standard deviation better than mean ?
enerally more useful as it is calculated with reference to the spread around the Mean value
what's the SD formula?
whats the variance of data?
give by s^2
How to calculate relative standard deviation?
100 x S/mean %
what is RSD used to measure?
relative precision of different sets of measurements