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

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

4. 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

5. 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

6. 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

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