1. A radical view on plots in analysis
Hein Stigum
Presentation, data and programs at:

2. Agenda Why use graphs Common use A graphic evolution Plots in analysis
Mar-18
H.S.

3. Why use graphs?

4. Problem example Lunch meals per week
Table of means (around 5 per week)
Linear regression
Mar-18
H.S.

5. Problem example 2 Iron level
Linear regression: Males 9.4 units higher iron level
Logistic regression: Males 10.4 times more anemia
In linear regression: constant variance is rejected (p<0.0001) , but that is another matter
Low Iron: 1.1%
Mar-18
H.S.

6. Problem example 3 Weight on blood pressure Missing sex Mar-18 H.S.
Crude (outlier removed): 23.1
Adjusted: 20.6
Positive bias as expected
Missing sex
Mar-18
H.S.

7. Common use

8. Pie and bar
Mar-18
H.S.

9. Bar-Dot-Line evolution
Last plot: can compare both within and across groups
Need 2 versions of bar plots to do that
Mar-18
H.S.

10. The workhorses: Scatter and density

11. Scatterplot
Main effect: line
Non-linearity's: curve
Outliers: Points

12. Density
Density
kdensity weight
Boxplot
graph hbox weight
Mar-18
H.S.

13. Density with “boxplot” information
Mar-18
H.S.

14. Scatter and density plots for many types of data
x-normal use
x-suggested use
Mar-18
H.S.

15. Plots in analysis

16. Continuous outcome

17. Continuous by 1 category
Mar-18
H.S. 17

18. Continuous by 2 categories
Is birth weight the same for boys and girls?
Scatterplot
Density plot
Sdtest for equal variance: p=0.13, equal variance
Equal means? Linear effect?
Outliers?
Equal variances?

19. Continuous by 3 categories
Is birth weight the same over parity?
Scatterplot
Density plot
Scatter to see linear/no-linear effect, look for outliers
Density to see equal variance
Equal means? Linear effect?
Outliers?
Equal variances?
Mar-18
H.S.

20. Continuous by continuous
Does birth weight depend on gestational age?
Scatterplot
Density plot
Fpfitci plus lfit gives a graphic test of linearity
Equal means? Linear effect?
Outliers?
Mar-18
H.S.

21. Binary outcome

22. Binary by 2 categories Does the low birth weight depend on sex? Jitter
and
line

23. Binary by 3 categories Does the low birth weight depend on parity?
Linear on a linear scale, but for small effect, also linear on a log scale
(using a log scale does not work), fracpoly logit y x1 x2 x3 followed by fracplot will work

24. Binary by 3 categories, no scatter
Does the low birth weight depend on parity?
Proportions: 7.2% 3.7% 3.2%, chisqr p-val=0.12, nptrend p-val 0.06

25. Scatter: binary by countinuous
Does the low birth weight depend on gest. age?
For strong effects line and curve may go outside 0-1
Mar-18
H.S.