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Haldna presentation

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  • 1. professor of Psychology Rand R.Wilcox, University of Southern California Written by Marina Haldna
  • 2.
    • To introduce and compare different statistical methods
  • 3.
    • Introduction
    • Methods
    • Results
    • Conclusion
  • 4.
    • Typical situatsions :
    • before-after
    • two places with parallel measurements
    • Every pair of sampled data has a important information to make a correct conclusion
  • 5.
    • Data are missing at random.
    • The reason why a data point is missing is not related to its actual value
  • 6.
    • Simple strategy is to compute a confidence interval using a normal or t-distribution, this approach may be unsatisfactory (Liang et al. 2008)
    • Even if there are non-missing data, low power arise when sampling from a heavy-tiled distribution (Wilcox, 2005)
  • 7.
    • Median
    • 20% trimmed mean
    • Difference between the marginal trimmed means
  • 8.
    • M1(means)
    • M2(trimmed means)
    • M3 –bootstrap method with trimmed means
    • M4-medians
    • In terms of efficiency, the median generally performs better than 20% trimmed mean (Wilcox,2006)
  • 9.
    • To check the properties of the methods , one sample of correlated and an other non-correlated data from bivariate distribution were used
    • Simulations were repeated 3000 times, sample size was taken 30.
    • Two different cases for missing dates:
    • 5 from one and 5 from an other group
    • 10 from one and 0 from an other group
  • 10.
    • In terms of Type I errors
    • The method for comparing means can be unsatisfactory
    • Percentile bootstrap method with 20% trimmed means performed well
    • In terms of power the M2 and M3 are more satisfactory
  • 11.
    • Statistics means never having to say you a re certain
    • Statistics is the art of never having to say you a re wrong
    • ( http://www.btinternet.com/~se16/hgb/statjoke.htm )
  • 12.  

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