1. Experimental Design
A Quick Overview

2. Variables
Independent variable – the variable that is manipulated or changed
The CAUSE of any differences you measure in the dependent variable
Dependent variable – the variable that responds to the change
Is the variable that is measured as you run the experiment

3. Variables
Constant – factors that remain the same for all trials and groups
Control – group that does not contain the independent variable (“No treatment group”)
Trials – the number of organisms/objects per group
Trials – the number of times the experiment is repeated

4. Hypothesis: Null vs alternative
Hypothesis: expected results from an experiment
Null hypothesis: the hypothesis which the researcher is trying to disprove, reject, or nullify
Often contains the “common” view that the researcher is trying to disprove
Alternative hypothesis: hypothesis that reflects the researcher’s beliefs of the phenomena

5. Hypothesis: Null vs Alternative
In an experiment conclusion, the researcher ALWAYS rejects or confirms the null
It is incorrect if the researcher claims to have proved or confirmed the alternative hypothesis, because there are other experimental steps to take

6. Hypothesis: Null vs Alternative
Examples:
Alternative hypothesis: (H1) Tomato plants exhibit a higher rate of growth when planted in compost rather than in soil.
Null Hypothesis: (H0) Tomato plants do not exhibit a higher rate of growth when planted in compost rather than soil.
Poor null hypothesis: (Not specific enough) Tomato plants show no difference in growth rates when planted in compost rather than soil. Read more: 

7. Hypothetico-Deductive Thinking

8. Writing Hypothesis If, then form
If … (Independent variable), then… (dependent variable)
Example:
Independent variable: type of soil substrate
Dependent variable: Growth of plant
Hypothesis: If wheat plants are planted in a compost-based substrate, then they will exhibit more growth than if they had been planted in a sand-based substrate.
Null hypothesis: If wheat plants are planted in a compost-based substrate, then they will not exhibit more growth than if they had been planted in a sand-based substrate.