Experimental Design A Quick Overview

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

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

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

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

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: http://www.experiment-resources.com/null-hypothesis.html#ixzz1WhJdivub

Hypothetico-Deductive Thinking

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.