AtlasSession 3L7: Systematic errorsp.22–29, 76–77
Confounder, mediator, moderator
- Study designs primer
- What is systematic error
- Confounding
- Confounder, mediator, moderator
Fig. 1
Rat calvarial defects: bone volume at 8 weeks, VEGF-releasing vs plain collagen scaffold (mm³, micro-CT)
Fig. 1: does the VEGF scaffold change the bone volume? A third factor: new blood vessels. The VEGF scaffold grows more blood vessels, and the vessels lead to more bone. Pick the role: on the path, behind both, or changes the size.
- Third factor
- New blood vessels
- Your answer
- pick a role (Press one of the three role buttons.)
Causal Diagram Lab · First look
Level 1 · First look · Lecture 7 · p.22–29, 76–77
Tell apart three ways a third factor can sit around a cause and its effect.
Classify a third variable as a confounder, mediator or moderator from how it relates to exposure and outcome, and explain why one factor can change role.
On the path (the step you are on)
Fertiliser → more leaves → more tomatoes; leaves carry the effect (mediator).
Fertiliser grows more leaves, and more leaves grow more tomatoes: the leaves sit on the path and carry the effect (a mediator). Third factor here: New blood vessels. Your answer: pick a role (Press one of the three role buttons.).