The Scientific Method Experimental Design A A plan

The Scientific Method (Experimental Design) A. A plan used to collect, organize and explain information (answers a question about an observation that was made) B. Based on: 1. Observations: data gathered with our 5 senses & scientific instruments 2. Inferences: interpretation of observations (conclusions)

The Make an observation Scientific (Problem) Ask a question Method (Testable Develop a hypothesis prediction) Test hypothesis with a controlled experiment Repeat experiment multiple times to obtain consistent results. Revise hypothesis and re-test Collect and analyze data and make conclusions Hypothesis is supported Hypothesis is not supported Potentially develops into a theory

C. Design a controlled experiment to test the hypothesis. 1. Only one variable is manipulated by the experimenter. (Everything else must be the same – constants) a. The independent variable (manipulated variable) is the one that the experimenter alters and that will cause change in another variable. Ex. The type of plant food given to each of 4 pea plants. *Constants: same amount of light, water, temperature etc. Food A Food B Food C Food D

b. The dependent variable (responding variable) is the one that changes in response to the independent variable (the results). Ex. Height of each of the 4 pea plants after a specific period of time. A B C D

2. Two test groups… use a LARGE sample size (lots of test subjects b. Control group: exposed to “normal” the independent variable is present/changed in this group conditions for comparison (lacks the independent variable) a. Experimental Group: Food A Food C Food B Food D Ex. A 5 th pea plant that does not receive any plant food…. . . only light, water etc.

*Control group may be given a placebo – substance containing no medicine, such as a sugar pill *In the conclusion, compare experimental group results to control group results

D. To Make an Experiment More Valid: 1. Repeat the experiment 2. Use a larger sample size (more specimens)