BHS 204-01Methods in Behavioral Sciences I

April 9, 2003

Chapter 2 (Stanovich) – Falsifiability: How to Foil Little Green Men in the Head

Logic of Experimentation Two forms of logic:

Deduction – moving from general principles to specific conclusions.

Induction – moving from specific observations to general principles.

Induction is used during naturalistic and exploratory research.

Deduction is used during experiments.

Propositional Logic Modus Ponens (confirmatory)

If p then q Observe p Conclude q

Modus Tollens (disconfirmatory) If p then q Observe not-q Conclude not-p

Logical Fallacies Affirming the consequent

If p then q Observe q Conclude p

Denying the antecedent If p then q Observe not-p Conclude not-q

Falsifiability Seeking support for hypotheses commits the

logical fallacy of affirming the consequent. Instead, we must test hypotheses by seeking

disconfirmatory evidence. A testable theory is one that can be proven

wrong – if it is wrong. It must have the chance to fail. A theory cannot explain every outcome.

Popper’s Approach Predictions from theory (hypotheses) must be

specific. They must state what will happen and what will

not happen. General predictions or all-encompassing

predictions cannot be tested (are unfalsifiable). When data accumulates that contradicts

theory, then theory must be changed. Data is not thrown out – explanations are.

Two Hypotheses Null hypothesis (H0):

There will be no difference between treatment and control groups (no treatment effect).

Alternative hypothesis (H1): There will be a difference of a particular kind. Directionality – states how the treatment group

will differ from the control group. We test the null hypothesis and by rejecting it

(disconfirming it) can accept the alternative.

The Neyman-Pearson Approach Two theories can be compared by predicting

incompatible outcomes: If theory A is correct, hypothesis A will be

confirmed and B will be disconfirmed. If theory B is correct, hypothesis B will be

confirmed and A will be disconfirmed. The comparison is not with the control group

( is there a treatment effect or not) but with the predictions made by the two theories.

Errors are Important We learn something, even when an

experiment does not “work” – does not produce the expected result. Knowledge advances when we find that our ideas

are wrong and can abandon incorrect beliefs. We must be willing to let evidence guide belief –

not the other way around. Scientists criticize each other’s ideas in an

ongoing dialectic that produces change.

Working on the Fringes Interesting questions are those that:

Exist at the fringes of knowledge. Can be tested using existing methods.

Many questions are important but untestable. Some questions are interesting to the public

but not to scientists because they have already been answered: ESP and other paranormal claims, astrology.