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

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

3. 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
Ex. The type of plant food given to each of 4 pea plants.
*Constants:
one that the experimenter alters and that will cause change in another variable.
same amount of light, water, temperature etc.
Food A
Food B
Food C
Food D

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

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

6. *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

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