Review of some terms Variable – anything that affects the results of an experiment Independent variable (IV) – specific variable being changed Dependent variable (DV) – specific variable being measured Constants (controlled variables) – all other variables that need to remain constant

Causal Question Starts with “why” Answer to causal question requires an explanation The answer should NOT be what you get as results for your experiment Do not use the words “affect” or “effect”

NOT a Causal Question How does light affect the growth of plants? Does not require an explanation of why there is an effect “light” is not an independent variable; must be specific, i.e., quantity of light, wavelength of light … “growth” is not a dependent variable; what will be measured? What plant is being tested?

A good causal question Why do Phaseus vulgaris plants grown in different wavelengths vary in the number of flowers produced? Requires an explanation involving the physiology of the plant Specific as to what will be done with light  wavelength (IV) DV is clear  number of flowers