When Small Effects are ImpressiveDeborah Prentice &

Dale Miller

Or…

Don’t mess with the bunny

Don’t mess with the bunny

VS

Big Impressive effect size bunny

It may look like a small potatoBUT

It’s actually quite impressive…

Small Potato effect

It resembles a duck!

Outline

Question: How do we know when a result is important?

Answers:

1. Size Matters- Standard Practice: measure statistical strength

2. Some things other than size matter- Method matters

Size Matters

• Statistics quantify the size of an effect

• Standardized measures are useful• Values are meaningful• Results can be compared across studies• But more importantly:

• We can quantify how Large and dreamily important the effect is!

• Large effects are impressive!

• But size is not the only thing that matters!

Size doesn’t matter

• Small effect can be really impressive – If no effect is expected, a small effect is a huge

deal

• Method matters • Alternative ways to demonstrate

“impressiveness”– Minimal manipulation of independent variable– Difficult to influence dependent variable

Minimal Manipulation

• What makes this design impressive:– The manipulation of the IV is so slight

that it shouldn’t account for any dependent variable variance

… but it DOES

• Studies low on manipulation, high on interesting-ness, low on effect size:– Minimal group experiment– Mere exposure effect– Cookie = happy helper

Difficult to influence DV• How does this design make a small

effect impressive?– The dependant variable should be resistant toexperimental manipulations…But it’s NOT

• Examples:– Judicial decisions and attractiveness – Conformity to group pressure

Summary

1. Statistics can quantify effect size

2. Important-ness of effect not equivalent to large-ness of effect

3. Small effects can be super impressive

4. Small effects are impressive when theIV shouldn’t affect the DV, but it does

Conclusions

Small potato wins sometimes

Conclusions

Small potato wins sometimes

Thank you!

http://www.youtube.com/watch?v=6uLUVI3Y0q0