Experimental design:


Methods and techniques in psychology:

Why is psychology a science?

"Science" involves using the scientific method:

Testable (falsifiable) hypotheses and theories (hence precise operational definitions of phenomena).

Empirically-obtained, publicly-available and replicable data (hence usually quantitative measurements).

Identification of causal relationships.

Parsimony ("Occam's razor").

Healthy scepticism.

Objectives of science:

Description, Explanation, Prediction.

Science versus pseudoscience:

Science: Pseudoscience:


Claims open to scrutiny and refutable

All evidence is considered,for and against claims

Based on appeals to authority, e.g. "wisdom of the ancients"

Adherents protect claims from disproof

Only apparently-corroborative evidence is considered

Phenomena often unreplicable Observable, replicable phenomena

Scepticism encouraged Scepticism discouraged

Parsimonious, and consistent with existing science

Develops over time

Non-parsimonious, often inconsistent with existing science


Objectivity: the need for operational definitions:

Many psychological phenomena are poorly defined and/or have "folk psychology" definitions: e.g. play, aggression, anxiety, arousal, fatigue, frustration, intelligence.

Operational definitions are in terms of the processes needed to measure the phenomenon .

e.g. "social play" = "wrestling behaviour between two young animals, accompanied by 'play signals' (exaggerated gait, inhibited biting) and unaccompanied by deliberate infliction of injury by either participant".

Game of

Scrabble, old chap?

Mmm, don’t mind if I do, old bean!

Definition of autism:


A. A total of six (or more) items from (1), (2), and (3), with at least two from (1), and one each from (2) and (3)

1. Qualitative impairment in social interaction, as manifested by at least two of the following: a) marked impairments in the use of multiple nonverbal behaviors such as eye-to-eye gaze, facial expression, body posture, and gestures to regulate social interaction.

b) failure to develop peer relationships appropriate to developmental level.

c) a lack of spontaneous seeking to share enjoyment, interests, or achievements with other people,

(e.g., by a lack of showing, bringing, or pointing out objects of interest to other people).

d) lack of social or emotional reciprocity (e.g. not actively participating in simple social play or games, preferring solitary activities, or involving others in activities only as tools or "mechanical" aids).

2. Qualitative impairments in communication as manifested by at least one of the following: a) delay in, or total lack of, the development of spoken language (unaccompanied by an attempt to compensate through alternative modes of communication such as gesture or mime).

b) in individuals with adequate speech, marked impairment in the ability to initiate or sustain a conversation with others.

c) stereotyped and repetitive use of language or idiosyncratic language.

d) lack of varied, spontaneous make-believe play or social imitative play appropriate to developmental level.

3. Restricted repetitive and stereotyped patterns of behavior, interests and activities, as manifested by at least two of the following: a) encompassing preoccupation with one or more stereotyped and restricted patterns of interest that is abnormal either in intensity or focus.

b) apparently inflexible adherence to specific, nonfunctional routines or rituals.

c) stereotyped and repetitive motor mannerisms (e.g hand or finger flapping or twisting, or complex wholebody movements).

d) persistent preoccupation with parts of objects.

B. Delays or abnormal functioning in at least one of the following areas, with onset prior to age 3 years:

(1) social interaction.

(2) language as used in social communication.

(3) symbolic or imaginative play.

C. The disturbance is not better accounted for by Rett's Disorder or Childhood Disintegrative Disorder.

Objectivity: the need for precise measurement:

Independent variable - the thing you manipulate, as an experimenter.

Dependent variable - the thing you measure.

e.g.: effects of status on initial interaction distance (Dean, Willis and

Hewitt 1975)

IV: status - operational definition: military rank

DV: interaction distance - operational defnition: number of floor squares between interactors (various settings, all with standard floor-tile size)

Inter-observer reliability checked

Results: status affected interpersonal distance: initial distance was higher when a lower-rank person approached a higher-rank person, than when peers met or a higher-rank person approached a lowerrank person

Objectivity: the need to avoid experimenter effects:

Huge literature on how experimenters can bias results

(Rosenthal 1966).

Ways to minimise these effects:

Precise definitions of IV's and DV's.

Standardised instructions and procedures.

Double-blind techniques.

Independent replication.

Theories and data:

Theories integrate and summarise scientific facts.

Give rise to hypotheses - specific predictions.

Interaction between theory and observation: theory guides observation, observation modifies theory theory hypothesis test (observation, experiment) revise theory mental activity affects brain health listening to Beyonc é rots your brain

(a) study Beyonc é fans, or

(b) experiment - listeners vs non-listeners hypothesis test (observation, experiment) only long periods of exposure have ill-effects

prolonged mental activity affects brain health

History of psychology:

19th c.: introspective methods - results open to dispute.

Early 20th c.: Behaviourism - restriction to purely behavioural measures that are amenable to quantitative analysis.

Late 20th c.: behavioural data used as an indirect measure of unobservable internal states (e.g. RT as an i ndex of processing speed in cognitive psychology).

History of neuropsychology:

19th c.: detailed qualitative single-patient case studies.

Problem - results open to different interpretations.

Early 20th c.: quantitative group studies.

Problem - group performance does not necessarily reflect individual performance.

Late 20th c.: detailed quantitative single-patient case studies. Descriptions of patients supported by quantitative data (plus statistical comparisons of patient to group norms).

Tinbergen (1963): four "whys":

Ultimate and proximate causes of behaviour.

1. Function (adaptation: ultimate cause)

2. Causation (proximate cause)

3. Ontogeny (development: proximate cause)

4. Phylogeny (evolutionary history: ultimate cause) e.g. Why do starlings sing? (1) To attract mates to breed. (2)

Increasing day-length affects hormone levels. (3) They learn to sing from their neighbours. (4) Song has evolved from simpler songs in ancestral bird species.

Psychology has traditionally focused on 2 and 3, neglecting 1 and 4.

Methods used in psychology:

Advantages Disadvantages


Interviews, Case

Studies and



Naturalistic behaviour.

Time-consuming. Unlikely to reveal causal relationships.

In-depth, detailed information.

Best way to establish causal relationships

Reporting bias.

Lack of self-insight.

Data sometimes too closely tied to theory.

Artificial (ecological validity)

Participant representativeness.

is it safe to use a mobile phone while driving?:

Advantages Disadvantages


(accident statistics)


Case Studies and



Information on realworld risks.

In-depth, detailed information.

Accidents involving phones are rare (Violanti

1998: 5 users out of sample of 223,137 accidents !

Reporting bias (Chapman and Underwood 2000:

80% of near-accidents forgotten within 2 weeks).

Best way to establish

how phoneuse might increase risk of accident.

Simulators cannot simulate real risks of driving; real-world studies are unethical.

Artificial tasks, in terms of content and timing of conversation.

Participants often unrepresentative.

Problems with correlational techniques:

Does smoking cause cancer?

Strong correlation between smoking and cancer -but does smoking cause cancer?

Alternative explanations:

Cancer-prone people are attracted to smoking.

Stress causes people to smoke and to develop cancer.

Correlations usually have too many alternative explanations.

The experimental method is the best way of identifying causal relationships.

X causes Y if:

X occurs before Y

Y happens in the presence of X

Y does not happen in the absence of X

The "Mozart Effect": babies that listen to Mozart before birth are supposedly more intelligent as children.

X (listening to Mozart) is associated with Y (intelligence).

What causes the change in intelligence?

To demonstrate a causal relationship, need to show that

(a) listening to Mozart precedes the change in intelligence (X precedes Y);

(b) the change in intelligence occurs when babies listen to Mozart (Y happens in presence of X);

(c) the change in intelligence does not occur when babies do not listen to Mozart (Y does not happen without X: i.e. other explanations can be ruled out).

Alternative explanations for the Mozart effect:

1. Listening to Mozart directly affects intellligence by stimulating neural development.

2. Babies who listen to Mozart have better - educated parents (more interested in their children's development and education).

3. Babies who listen to Mozart have better - educated parents (wealthier and therefore healthier).

3. Mothers who listen to Mozart are more relaxed; somehow this affects the baby's neural development.

4. Babies who listen to Mozart are more relaxed; somehow this affects their neural development.

Good experimental designs enable us to eliminate some of these alternative explanations:

To establish causality we use groups that differ systematically only on one variable (the independent variable) and measure the effects of this on an outcome variable (the dependent variable).

Pick pregnant women who do not differ systematically on any variables (age, musical preferences, SES, health, etc.).

Randomly assign half to listen to Mozart, and half to listening to something else.

Measure the children's intelligence: systematic differences between groups are probably due to the mothers' different experiences (i.e. Mozart/ no Mozart).

Experiment to test the Mozart effect:

The ONLY systematic variation between experimental and control groups is exposure to Mozart: worrying, happiness, motivation, irritability, etc. vary randomly (unsystematically) between groups

Why do we use statistics?

Most studies compare groups -

Behaviour often shows variability: hence individual performance may be atypical.

Individuals in a group vary randomly around "average" performance.

Compare average of one group to average of another.

Why do we use statistics?

Exceptions -

Behaviourist studies.

Psychophysical studies.

High degree of control over behaviour reduces variability and enhances replicability of findings.

Typical patterns of leverpressing in response to different schedules of reinforcement

The kinetic depth effect

Effects of frame-to-frame distance between dots on perception of depth

Disadvantages of the experimental method:

Intrusive - participants know they are being observed, and this may affect their behaviour.

Experimenter effects.

Not all phenomena are amenable to experimentation, for practical or ethical reasons (e.g. post-traumatic stress disorder, near-death experiences, effects of physical and social deprivation, etc.)

Some phenomena (e.g. personality, age or sex differences) can only be investigated by methods which are, strictly speaking, quasi-experimental.


Experiments are a useful tool for establishing cause and effect - but other methods (e.g. observation) are also important in science.

A good experimental design ensures that the only variable that varies is the independent variable chosen by the experimenter - the effects of alternative

confounding variables are eliminated (or at least rendered unsystematic by randomisation).

"Science" is mainly defined not by what you study, but by how you study it.