Transcript The Scientific Method

The Scientific Method
Observe a
Phenomenon
Confirm / Re-examine
Not
Prove or Disprove
Carefully study it.
Systematic Observation
& Measurement
Develop a theory to
explain the data
Check the implications of your
theory against new data from
similar
circumstances
Necessary & Sufficient
Conditions
• A is said to be a sufficient condition for B.
If A happens B will be guaranteed to occur.
• EX: Ceteris Paribus, if it rains then the
football field will be wet. Necessary &
Sufficient Conditions.
A B
Testing Causality
• If A is observed and ceteris paribus B does
not occur then the idea that A causes B is
called into question.
• EX: Theory: C.P. Price is negatively related
to quantity demanded.
– We observe price falling and ceteris paribus
quantity demanded also falls. Does the data
support the theory?
Testing Causality
• Econometrically we can estimate an
equation for demand.
• Q = f(Price, Income, Other Variables)
• What is the predicted sign on the coefficient
of price? (Is it significant?)
Fallacies
• Denying the antecedent:
~ A ~ B
It did not rain therefore the football field cannot
be wet (How about a sprinkler system?)
• Affirming the consequent:
B A
The field is wet therefore it must have rained.
(Sprinklers may have been on)
Contrapositive
• The only logical equivalent to A=> B is the
contrapositive statement ~B => ~A.
• EX1: If it rains then the field will be wet.
(Contrapositive) The field is dry therefore it did not rain.
• EX2: If cigarettes are addictive then past
consumption influences present consumption.
(Contrapositive) If past consumption does not influence
present consumption then cigarettes are not addictive.