The scientific method involves making observations, formulating hypotheses to explain those observations, and testing hypotheses through experiments. If experimental results support a hypothesis, it may become a theory. Theories that have withstood extensive testing and are widely accepted may become scientific laws that describe fundamental principles of nature. The scientific community shares and evaluates findings through peer-reviewed journals, conferences, and collaboration.

1. THE SCIENTIFIC METHOD

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The Scientific Method: Observation
• An observation is a thoughtful and careful
recognition of an event or a fact.
• The careful observation of a phenomenon
leads to a question.
– How does this happen?
– What causes it to occur?

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The Scientific Method:
The Hypothesis
• Hypothesizing
– question an observation
– propose possible solutions to questions based on
what is already understood about the phenomenon
• Hypotheses must:
– be logical
– account for all current information
– make the least possible assumptions
– be testable

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Testing Hypotheses
• Hypotheses need to be tested to see if they are
supported or disproved.
– Disproved hypotheses are rejected
– Hypotheses can be supported but not proven
• Ways to test a hypothesis:
– Gathering relevant historical information
• Retrospective Studies
– Make additional observations from the natural world
– Experimentation

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The Scientific Method:
Experimentation
• Experiments
– rigorous tests to determine if the solutions are
supported
• Experiments attempt to recreation an occurrence
– tests whether or not the hypothesis can be supported
or rejected
• There are many types of experiments
– laboratory, clinical trials, surveys, statistical analyses

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Experimental Design
• Experiments must:
– use large numbers of subjects and/or must be
repeated several times (replication)
– be independently reproducible
• The validity of experimental results must:
– be tested statistically
• chi-squared test for statistical significance
– be scrutinized by other scientists
• peer reviewed

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Experimental Design
• Experiments must:
– use large numbers of subjects and/or must be
repeated several times (replication)
– be independently reproducible
• The validity of experimental results must:
– be tested statistically
• chi-squared test for statistical significance
– be scrutinized by other scientists
• peer reviewed

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Theory
• If the hypothesis is supported by ample experimental data, it
leads to a theory.
• A theory may be defined as a widely accepted, plausible general
statement about a fundamental concept in science.
– The germ theory states that infectious diseases are caused by
microorganisms.
• Many diseases are not caused by microorganisms, so
we must be careful not to generalize theories too
broadly.
– Theories continue to be tested
• Exceptions identified
• Modifications made

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A Scientific Law
• A scientific law is a uniform and constant fact of nature that
describes what happens in nature.
– An example: All living things come from pre-existing living things.
• Scientific laws promote the process of generalization.
– Inductive reasoning
– Since every bird that has been studied lays eggs, we can generalize that all
birds lay eggs.
• Once a theory becomes established, it can be used to predict
specific facts.
– Deductive reasoning
– We can predict that a newly discovered bird species will lay eggs.

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Scientific Communication
• Data is shared with the scientific
community through research
articles published in scientific
journals.
– peer review
• Scientists present preliminary data
at conferences.
• Scientists collaborate directly by
phone and
e-mail.