scientific method and experimental design

Scientific Method

Hypothesis

Controlled Experiment and Variable

Independent and Dependent Variable

Sample Size and Validity

Scientific Method and Experimental Design

Steps of the Scientific Method

1. Make observations.

2. Ask a question.

3. Form a hypothesis.

4. Test the hypothesis.

5. Analyze the results.

6. Draw conclusions.

7. Communicate the results.

Hypothesis

An explanation of a natural event or observation that can be tested by additional observations or experimentation

Example of Hypothesis

Observation: The population of tiger salamanders declined 65% between 1984 and 1988

Hypothesis: Acids that were formed in the upper atmosphere by pollutants were falling onto mountains in the winter snows

Controlled Experiment and Variable

Tests one variable at a time (experimental variable)

Controlled experiments include 2 groups:

Experimental Group

Exposed to experimental variable

Control Group

Not exposed to experimental variable

Independent and Dependent Variables

Independent variable: The factor that is deliberately manipulated in an experiment (also called experimental variable)

Dependent variable: The variable that is changed or determined by manipulation of the independent variable. It is what is measure in the experiment

Sample Size

Sample Size (N)

•The number of subjects involved in experimentation

•Increasing N

• Decreases impact of chance events and error

• Increase reliability of results

Validity

The extent to which experimental results can be generalized to other settings or situations

To increase validity, increase N