1. Data Screening: Don’t Leave Home Without It
AEA Coffee Break Webinar
8 September 2011
Dale Berger

2. Why screen data? Locate and correct errors
Assure that assumptions of statistical procedures are met
Become familiar with the data
Context is critical

3. Bivariate data example
Data constructed by Anscombe consists of four sets of 11 pairs of X-Y scores. Can these four sets of data be pooled? Bumble applied regression to each set separately and recorded summary statistics.
Anscombe, F. J. (1973). Graphs in statistical analysis. The American Statistician, 27,

4. These summary statistics are identical in all four sets
Sample Size (N) 11
Mean of X
9.0
Mean of Y
7.5
Correlation
0.816
Linear Equation
y′ = x
Regression SS
27.50
Residual SS
13.75 (df = 9)

5. Bumble’s Conclusions:
There is a strong linear relationship between X and Y, as is apparent from r = .819, F(1, 9) = 18.00, p=
All four data sets are equivalent and probably were sampled from the same population.
What more would you like to know?

6. Anscombe’s four data sets

7. Data Set 1

8. Data Set 2

9. Data Set 3

10. Data Set 4

12. You can see a lot by just looking ---Yogi Berra
If you don’t look, you won’t see it.
--- DB

13. The Most Important Test in Statistics
The Intra-Ocular Trauma Test
To err is human; to really screw up it takes a computer!

14. Thank you! Questions and comments? dale.berger@cgu.edu