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Stata 2, Bivariate

Stata 2, Bivariate. Hein Stigum Presentation, data and programs at: http://folk.uio.no/heins/. Aug-14. H.S. 1. Datatypes. Categorical data Nominal: married/ single/ divorced Ordinal: small/ medium/ large Numerical data Discrete: number of children Continuous: weight. Aug-14.

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Stata 2, Bivariate

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  1. Stata 2, Bivariate Hein Stigum Presentation, data and programs at: http://folk.uio.no/heins/ Aug-14 H.S. H.S. 1

  2. Datatypes • Categorical data • Nominal: married/ single/ divorced • Ordinal: small/ medium/ large • Numerical data • Discrete: number of children • Continuous: weight Aug-14 H.S. H.S. 2

  3. Data type dictates type of analysis Aug-14 H.S. H.S. 3

  4. Continuous symmetric outcome Example: Birth weight Aug-14 H.S. H.S. 4

  5. Distribution kdensity weight drop if weight<2000 kdensity weight Aug-14 H.S. H.S. 5

  6. Central tendency and dispersion Mean and standard deviation: Mean with confidence interval: Aug-14 H.S. H.S. 6

  7. Equal Not equal Compare groups, equal variance? Aug-14 H.S. H.S. 7

  8. 2 independent samples Are birth weights the same for boys and girls? Density plot Scatterplot Aug-14 H.S. H.S. 8

  9. 2 independent samples test Aug-14 H.S. H.S. 9

  10. K independent samples • Is birth weight the same over parity? Density plot Scatterplot Equal means? Linear effect? Outliers? Equal variances? Aug-14 H.S. H.S. 10

  11. equal means? Equal variances? K independent samples test Aug-14 H.S. H.S. 11

  12. Does birth weight depend on gestational age? Continuous by continuous Scatterplot Scatterplot, outlier dropped Aug-14 H.S. H.S. 12

  13. Continuous by continuous tests • Cut gestational age up in groups, then use T-test or ANOVA or • Use linear regression with 1 covariate Aug-14 H.S. H.S. 13

  14. Test situations • 2 independent samples • ttest weight, by(sex) • K independent samples • oneway weight parity • By continuous • regress weight gestAge • 2 dependent samples (Paired) • ttest weight_last_year = weight_today Aug-14 H.S. H.S. 14

  15. Continuous skewed outcome Example: Number of sexual partners Aug-14 H.S. H.S. 15

  16. Distribution kdensity partners if partners<=50 Aug-14 H.S. H.S. 16

  17. Central tendency and dispersion Median and percentiles: Aug-14 H.S. H.S. 17

  18. 2 independent samples Do males and females have the same number of partners? Scatterplot Density plot Aug-14 H.S. H.S. 18

  19. equal medians? 2 independent samples test Aug-14 H.S. H.S. 19

  20. K independent samples Do partners vary with age? Scatterplot Scatterplot (partners<20) Density plot (partners<20) Aug-14 H.S. H.S. 20

  21. equal medians? K independent samples test Aug-14 H.S. H.S. 21

  22. Table of tests Categorical ordered: use nonparametric tests Aug-14 H.S. H.S. 22

  23. Categorical data Example: Being bullied Aug-14 H.S. H.S. 23

  24. Frequency and proportion Frequency: Proportion with CI: Aug-14 H.S. H.S. 24

  25. Proportion, confidence interval proportion: standard error: confidence interval: x=”disease” n=total number Aug-14 H.S. H.S. 25

  26. equal proportions? Crosstables Are boys bullied as much as girls? Aug-14 H.S. H.S. 26

  27. Ordered categories, trend Does bullied vary with age? twoway (fpfitci bullied agegr) /// (lfit bullied agegr) H.S.

  28. Trend? equal proportions? Ordered categories, trend Aug-14 H.S. H.S. 28

  29. Table of tests Categorical ordered: use nonparametric tests Aug-14 H.S. H.S. 29

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