FAQ/distFAQ - CBU statistics Wiki

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Questions about distributions of random variables

  1. How many observations do I need to make z-scoring (assuming Normality) feasible?

  2. Are there any on-line statistical tables for commonly used distributions?

  3. Why are the degrees of freedom not whole numbers?

  4. What is the relationship between the z, t, chi-square and F distributions?

  5. A Normalising transformation of ratios of form (L-R)/(L+R)

  6. What is the probability of a repetition in a sequence of size k taken from K stimuli?

  7. How do I evaluate Multinomial probabilities of pooled trial frequencies of locations of peaks which can occur in one of K positions in each trial?

  8. How do I fit a Weibull distribution to scores over time using MATLAB and notes on using non-linear least squares?

  9. How do I recode levels of a group variable in SPSS?

  10. What is an intention to treat analysis?

  11. How do I evaluate a number to a general power in SPSS?

  12. A note on comparing confidence intervals and statistical significance

  13. How do I obtain a pooled standard error of the mean?

  14. How do I obtain the standard deviation from the standard error of the mean (s.e.m.) and how does this and the mean vary with sample size?

  15. What is the variance of the mean of my transformed data and the variance of combinations of means?

  16. How do I do a t-test between two weighted means?

  17. What is the relationship between the mean and the median from a sample and how do I compute 95% CIs for the median?

  18. What is an optimal cut-off for the discretization/splitting of a continuous variable and how do we use this in a regression?

  19. A quick approximation for Normally distributed expected order statistics

  20. How do I convert a z-score into a percentile in SPSS?

  21. How do I derive an expected total for a subset of items based on the expected overall total?

  22. How do I compute a difference in errors adjusted for overall number of errors when the errors have different signs?

  23. Residuals and (Non-)Normality

  24. How do I check Normality assumptions in repeated measures analyses in SPSS?

  25. Testing normality including rules of thumb for skew, kurtosis in SPSS

  26. Methods of handling outliers.

  27. How do I produce truncated exponential random variables using MATLAB?

  28. How do I obtain parameter estimates for finite Normal mixture distributions using SPSS and BMDP?

  29. How do I find out how many people have a score above a certain value?

  30. How do I compute percentile thresholds for exponential data and use in outlier detection?

  31. How do I generate a random sample in EXCEL?

  32. Matching groups and randomized allocation to groups

  33. Some thoughts on testing for randomness

  34. How do I obtain the mean of several variables, each minus the same constant? (In SPSS)

  35. How do I compute z-scores in SPSS and what is their relationship to comparing group means?

  36. Why does my t-statistic have a negative sign?

  37. How do I use cumulative distribution functions to compute p-values in SPSS, EXCEL and R?

  38. How do I adjust for age in comparing survival times in two different groups?

  39. What is the relationship between intercept and slope for scores at two time points?

  40. Arctan functions in EXCEL.

  41. How do I obtain statistical distributions in MATLAB?

  42. How do I produce random variables which follow a negative skew distribution?

  43. How do I calculate probabilities involving the multivariate normal distribution?

  44. Simulations sampling from data with replacement (bootstrapping)

  45. Bootstrapping without replacement (Secret Santa) in R

  46. Generating multivariate data with a required correlation matrix

  47. How do I obtain the formulae behind statistics outputted by SPSS algorithms?