1. The effect of third variables: thinking about trivariate hypotheses
Henk van der Kolk

2. Aim
Theorizing about potential ‘third’ variables. Introducing the word ‘trivariate’.

3. Testing bivariate hypothesis is checking:
time order of cause and effect
correlation/association
effect of third variables
Theorizing about the effect of third variables
Formulating a trivariate hypothesis
Testing the trivariate hypothesis

4. Example
Explaining obesity
Obeesety

5. example
Does social class (income/education) have a negative effect on obesity of individuals?
Social Class
Obesity -

6. Testing bivariate hypothesis is checking:
time order of cause and effect
correlation/association

7. Education
Source:

8. Testing bivariate hypothesis is checking:
time order of cause and effect
correlation/association
effect of third variables
Theorizing about the effect of third variables
Formulating a trivariate hypothesis
Testing the trivariate hypothesis

9. Potential effects of ‘third variables’
Moderator?
Independent variable
Dependent variable
Confounder?
Intervening variable?
Another independent variable?

10. - + Social class Obesity Addition: another independent variable
Level of metabolism
(genetics)
MeTAbolism

11. - _ + Social class Obesity confounding: a confounDing variable
Self constraint
Ability to plan
(genetic?)

12. - - + Social class Obesity interpretation: an intervening variable
Knowledge
about
consequences

13. Confounding or interpretation?
Time order: If the (original) independent variable precedes the third variable in time: interpretation. If the (original) independent variable is explained by the third variable: confounding.

14. + - Social class Obesity interaction: modifying the relationship
Supply of ‘easy food’ +
Social class
Obesity -

15. Trivariate hypothesis
After the introduction of the third (test) variable (mention the third variable) The bivariate relationship (mention the original bivariate hypothesis) … (disappears, changes, remains the same) And the test variable is related to the other variables …. (outline the model)

16. The effect of third variables: thinking about trivariate hypotheses