Small N research

Many early psychology studies of small n

• Fechner - visual psychophysics• James - introspection • Piaget - child development (his 3 children)• Freud - case studies• Skinner - conditioning “Instead of studying a thousand rats for one hour each, or a hundred

rats for ten hours each the investigator is likely to study one rat for a thousand hours”

• Inductive -specific to general principles• Very little statistical analysis

Why small N

Averaging can be misleading - the data looks like nobody (subject validity failed)

May be better to look at each individually

Group data can smear or disguise differences

Could support or refute theory erroneously

• Participants are rare

• Memory research eg H.M.• Clinical impact eg Phineas Gage

• Study of expertise – eg chess masters• Rare disease/ disorder eg Capgras

syndrome

Even a single case study can challenge a theory or act as a source of new hypotheses about normal and abnormal behavior.

• Ramachandran’s pig

Problems

• No valid causal inference if extraneous variables uncontrolled (particularly n=1)

• Often naturalistic and treatments uncontrolled• Interactions hard to observe

• Observer bias (esp clinical therapist)• Generalizability depends on population variability

eg visual system vs personality

Case Studies

• intensive description of individuals• source of hypotheses and ideas

• clinical• child development• animal behaviorists• anthropology• criminology• neurology• sociology• bogus science (anecdote)

Designs

• Single case study

• Naturalistic observation, interviews, tests- usually detailed information about many aspects of one person often not easy to compare with another person

• Often good for generating ideas or customizing treatment

Baseline, AB, ABA, ABAB

• Baseline shows underlying variability gives basis for comparison

• Establish target behavior

• Researcher manipulates variable

• If can withdraw treatment then ABAB best

(finish on treatment – ethical)

Text eg

ABAC, ABACAB….

• Increase complexity designs

• Baseline Treatment Baseline Control

• Eg placebo

• Or

• Baseline Treatment1 Baseline Treatment2

Multiple baselines

• Time differences in baseline and treatment

• Same type of behavior in 2 or more people

• Two or more behaviors in same person - hair pulling and head banging

• Same behavior different settings - social responding at breakfast and lunch

text

Changing criterion

• Gradual approximation to ideal behavior

• Shaping – must be individual

• Eg Desensitization - reduce fear of snakes

• Or exercise and obesity