1. 2015 Schield SS Shortcuts V0C 1 by Milo Schield StatChat Feb 24, 2015 Slides at: www.StatLit.org/pdf/ 2015-Schield-StatChat-Slides.pdf Statistically-Significant Shortcuts

2. 2015 Schield SS Shortcuts V0C 2 Background & Goal Statistical significance is one of statistics’ big ideas. For Z-scores, statistical significance is a single value. For Chi-squared and the student-T, it is a function. For correlation and relative risk, its a complex function. We need to focus on “big ideas” in random sampling. Goal: To create “shortcut” formulas for statistical significance that are sufficient and memorable.

3. 2015 Schield SS Shortcuts V0C If |p2 - p1| > 1/Sqrt(n), then that difference is statistically significant Q.Has anyone seen this shortcut? Where? Yes! Seeing Through Statistics by Jessica Utts. Q. Anywhere else? 3 #1: Proportions Shortcut (SS)

4. 2015 Schield SS Shortcuts V0C 4 Chi-Squared 2(df+1) Has anyone seen this shortcut anywhere?

5. 2015 Schield SS Shortcuts V0C 5 Has anyone seen this shortcut anywhere? Shortcut Margin of Error for Correlation: 2/Sqrt(N)

6. 2015 Schield SS Shortcuts V0C 6 Consider two groups each of size n. Relative Risk: RR = p2/p1 RR>1 is statistically significant if RR-1 = 2/sqrt(k1) where k1 = n*p1 >4 Has anyone seen this shortcut anywhere? Relative-Risk Shortcut (SS)

7. 2015 Schield SS Shortcuts V0C 7 T-Z: Actual vs. Model Has anyone seen this shortcut anywhere?

8. 2015 Schield SS Shortcuts V0C What are the costs in teaching these sufficient shortcuts for statistical significance? 1.|p2-p1| > 1/sqrt(n) 2.Chi-squared: Χ 2 > 2(df+1) 3.Correlation: r > 2/sqrt(n-1) for n > 4 4.RRisk > 1+ 2/sqrt(k1): k1=n*p1, p1<p2 5.t-stat (2-tail): t > 1.645 + 2/sqrt(df-1) 8 Question