Hypothesis Controlled Experiment and Variable Independent and Dependent Variable Sample Size and Validity Scientific Method and Experimental Design

Steps of the Scientific Method Make observations. Ask a question. Form a hypothesis. Test the hypothesis. Analyze the results. Draw conclusions. Communicate the results.

Make observations.

Ask a question.

Form a hypothesis.

Test the hypothesis.

Analyze the results.

Draw conclusions.

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

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

Why does a good experiment need to have two parts, including a control? It isolates and tests the effects of one variable at a time Provides certainty that the change is due to the effect of the variable being tested

It isolates and tests the effects of one variable at a time

Provides certainty that the change is due to the effect of the variable being tested

Validity The extent to which experimental results can be generalized to other settings or situations To increase validity, increase N