Scientific Method and Experimental Design
Goal of Science
Steps of Scientific Method
Hypothesis
Independent and Dependent Variable
Experimental Design
Sample Size and Validity
Data Collection and Organization
Conclusions
The Characteristics of Science
Science
A process, based on observations and experimentation, that provides explanations of natural events or problems
Uses the scientific method
Conclusions rely on data and facts
Steps of the Scientific Method
1. Make observation
2. Question/problem
3. Background research
4. Hypothesis
5. Experiment/observe
6. Collect and analyze data
7. Conclusion
8. Retest
9. Publish
An possible explanation of a natural event or observation that can be tested by additional observations or experimentation
Must be testable!
Written as “If……., then……” statement
Hypothesis
Identify 2 crucial variables to write hypothesis
Independent variable: The factor that is deliberately manipulated in an experiment (also called experimental variable)
• “Presumed cause”
Dependent variable: The variable that changes in response to changes in the independent variable. It is what is measured in the experiment
• “Presumed effect or result”
Hypothesis
Hypothesis
Hypothesis is written as follows:
If independent variable, then dependent variable
Ex. If 100 grams of fertilizer is applied to a lawn, then the lawn will grow at a faster rate.
IV amount of fertilizer
DV rate of growth
Controlled Experiments
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, all variables held constant
All extraneous variables must be held constant in both groups!
Sample Size (N)
•The number of subjects involved in experimentation
•Increasing N
• Decreases impact of chance events and error
• Increase reliability of results (validity)
Sample Size
The extent to which experimental results can be generalized to other settings or situations
To increase validity, increase N
Ex. 7 tanks, 6 experimental and 1 control
Each tank has 100 single celled green organisms
All variables held constant except the light
Validity
Quantitative Data: numerical data
Ex. Measurement of depth in inches
Qualitative Data: descriptive data
collect with your senses
Ex. Color
Use data tables and charts to more effectively display data for analysis
Record and Analyze Data
Conclusion
Refers back to the hypothesis
“Supported” or “rejected”
Use data to support
If the same conclusions are supported over a long enough period of time they become theories
The Characteristics of Science
1. Based on the assumption that the natural world can be investigated and explained in terms we can understand.
2. Based on the results of controlled experimentation and observations.
3. The results must be repeatable and verifiable.
4. Must be refutable. If a hypothesis is not supported by evidence it must be rejected or re-worded