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xapharius phoenix

xapharius phoenix's Public Library

  • A 95% confidence interval does not mean that for a given realised interval calculated from sample data there is a 95% probability the population parameter lies within the interval, nor that there is a 95% probability that the interval covers the population parameter.[11] Once an experiment is done and an interval calculated, this interval either covers the parameter value or it does not, it is no longer a matter of probability. The 95% probability relates to the reliability of the estimation procedure, not to a specific calculated interval.[12] Neyman himself (the original proponent of confidence intervals) made this point in his original paper:[3]

  • If repeated samples were taken and the 95% confidence   interval computed for each sample, 95% of the intervals would   contain the population mean. Naturally, 5% of the intervals would   not contain the population mean.

  • For instance waterway tonnage, as tracked by the U.S. Army Corps of Engineers Navigation Data Center, indicates the monthly tonnage volume of goods traveling across the ocean and other major bodies of water, including the Great Lakes region. Sources such as the Association of American Railroads (AAR) Weekly Rail Traffic Summary provide statistics on the percent change in monthly rail carloads and intermodal units.

  • Nigeria’s oil resources, on which the country depends for more than 70 per cent of government revenues and more than 90 per cent of hard currency earnings despite the rapid growth of other sectors of the economy

  • If your variables are of incomparable units (e.g. height in cm and weight in kg) then you should standardize variables, of course. Even if variables are of the same units but show quite different variances it is still a good idea to standardize before K-means. You see, K-means clustering is "isotropic" in all directions of space and therefore tends to produce more or less round (rather than elongated) clusters. In this situation leaving variances unequal is equivalent to putting more weight on variables with smaller variance, so clusters will tend to be separated along variables with greater variance.


    A different thing also worth to remind is that K-means clustering results are sensitive to the order of objects in the data set. A justified practice would be to run the analysis several times, randomizing objects order; then average the cluster centres of those runs and input the centres as initial ones for one final run of the analysis.

  • More formally, do a depth first traversal of the tree and evaluate  inherited attributes on the way down and synthetic attributes on the  way up.  This corresponds to a an Euler-tour traversal
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