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location: FAQ / regFAQ

Questions about linear regression

  1. What does a number containing an 'E' signify?

  2. What is the relationship between the Pearson correlation and a simple regression estimate?

  3. What is the relationship between predictor variable correlations and the presence of a suppressor variable?

  4. How do I check for outliers in a simple regression with one predictor variable?

  5. What is heterogeneity of variance in SPSS Probit and Logit procedures?

  6. Why don't I see fiducial confidence intervals doing a probit analysis in version 16 of SPSS?

  7. Meta-analysis issues: 1) How do I measure publication bias? 2) How do I obtain a confidence interval for pooled estimates from sets of log odds, Cohen's d and Pearson correlations using a) meta-analysis and b) for Cohen's d as suggested for combining two studies to assess replication of a result?

  8. In ANOVA and Regression, what do the various different types of Sums of Squares mean, and does the choice matter?

  9. What is the variance of the mean of my transformed data?

  10. How do I work out the meaning of a significant interaction?

  11. How do I test for an interaction involving a continuous variable (moderation analysis)?

  12. What is the difference between a hierarchical and a stepwise regression? Also:a reference for an alternative, decision trees

  13. How do I perform a stepwise regression in SPSS involving interactions?

  14. Interpreting the intercept term in a regression when covarying out predictors of within-subject difference scores

  15. What is the importance of including an intercept term in the SPSS (between subjects ANOVA) univariate procedure?

  16. How do I obtain covariance terms involving the intercept term in a linear regression using SPSS?

  17. Are there any primer publications explaining rationale and application of single case studies?

  18. How do I compute linear trend coefficients for single cases?

  19. How do I construct dummy variables for use in SPSS linear regression?

  20. How do I compare a within subjects group difference to that of a single case?

  21. Can I do an analysis of covariance using a regression?

  22. How do I test whether one independent variable has an influence on a dependent variable other than via the mediation of a second independent variable? (Sobel Test)

  23. Can I fit two-way links between variables in a path model?

  24. How do I put a regression line on a scatterplot in SPSS Version 12.0 and above?

  25. Why does the R-squared change when I fix the intercept in my regression line from its least squares value?

  26. What is Collinearity in multiple regression, and what do I do about it?

  27. How do I find the condition number of a matrix using R?

  28. How do I convert a factor variable into a numeric in R?

  29. How do I perform a regression with a categorical outcome?

  30. How do I look for the best fitting model with an unknown changepoints on ordered data?

  31. Regression diagnostics for categorical variables

  32. What is the Wald statistic?

  33. How do I compute the standard error of X1 in a regression also featuring X2?

  34. How do I interpret a regression involving variables A and B-A in predicting an outcome?

  35. How do I test to see if a mean adjusted for a covariate equal zero within a single group?

  36. How do I compute the standard error of ''beta'' in a linear regression in SPSS?

  37. Residuals and (Non-)Normality

  38. How do I compute Akaike's and Bayesian information criteria (AIC, BIC) to compare regression models and how do I interpret them?

  39. How well does a regression line fit?

  40. Checking for outliers in regression

  41. Why are the standard errors so large in logistic regression?

  42. Can you recommend any statistical textbooks?

  43. Is there an optimal ratio of cases to predictor variables I should have before doing a regression?

  44. How do I perform all possible subsets regression in SPSS?

  45. How do I do power calculations in SPSS?

  46. What is the relationship between significance tests of regression coefficients and of correlation coefficients?

  47. How do I compute the semi-partial correlation coefficient in R?

  48. How do I compare two squared (semi-partial) correlation coefficients (R-squareds) from different samples?

  49. How do I compare two squared (semi-partial) correlation coefficients from the same sample?

  50. How do I adjust R-squareds for the number of predictors in a model?

  51. What are random effect and multilevel models, when do I use them and are there effect sizes?

  52. Where can I find our about using random effects (including multilevel) models in R (including obtaining proportion of variance explained by a variable) & in SPSS?

  53. What does an error message concerning the Hessian matrix suggest when running a mixed (random effects) model?

  54. What does 's' denote when used to describe a General Linear Model (GLM)?

  55. What is a Generalized Additive (Mixed) Model (GA(M)M) and when do I use it?