6: small n designs

Question 1

small n research (idiographic/ morphogenic)

Answer 1

Each subject = separate experiment

Use of within-subject designs

Presented data: individual subjects

Comparisons between subjects

Reliability is assessed by replication (repetition)

Question 2

where is the small n approach useful?

Answer 2

Assumption of minimal biological or psychological variability

*Much of neuroscience
*Psychophysics
*Cognitive and behavioural neuroscience
*Human clinical neuropsychology/neurology
*Clinical psychology
*Animal learning and cognition (tradition?)

Question 3

what is the small n approach useful

Answer 3

1. Constraints: availability, convenience
2. No need for generalization
3. Assumption of low biological variability
4. Interest in a very small layer of the population
5. Need to understand the process in time
6. Detailed comparison of subjects

Question 4

key principles in small n research

Answer 4

Consistent level: magnitude of treatment effects.

Consistent trend: unidirectional changes.

Stability: consistent level or consistent trend.

Search of temporal patterns: time series (analyses).

Search of spatio-temporal patterns: sequential analysis of
behaviour. Serial configuration of events and actions in time.

Question 5

what is the principle of experimental research

Answer 5

replication

Question 6

why does small n or single subject research work

Answer 6

Large number of observations per subjects: fluctuations average out.

Factors that can contribute to variability are controlled in a strict manner.

Focus on “powerful” variables with a clear effect: Effect sizes.

Question 7

problems with small n research

Answer 7

Similar problems as for within-subject designs
*Irreversible changes in the behaviours of the subjects induced by the experimental procedures.

Weak effects (from the IV) on the DV.

Unstable DV’s despite strong experimental control:
*Uncontrolled variables
*Extraneous variables

Question 8

types of designs

Answer 8

baseline designs

dynamic designs

discrete trial designs

Question 9

what are baseline designs

Answer 9

Typically what researches refer to when mentioning “single-subject designs”.

Question 10

types of dynamic designs

Answer 10

Good for moment-by-moment changes in behaviour

Question 11

what are discrete trial designs

Answer 11

Good for a focus on performance of individual subjects (e.g., psychophysics).

Question 12

issue to keep in mind with baseline designs

Answer 12

reliability&raquo_space;> would replication produce same (or very similar) results

The behaviour is analysed based on both within and between experimental treatments data.
* No averaging of the data!

Question 13

what is the baseline phase

Answer 13

Behavioural baseline needs to be established until a
stability criterion is reached.

Question 14

what is the experimental or intervention phase

Answer 14

expose the subject to each
treatment, until criterion is reached. Then repeat.

ABA(B) designs: baseline - treatment - baseline (- treatment).

This is an intra-subject replication where subjects are their own control(s) (as in group within subject designs)&raquo_space;> internal validity.

Question 15

reversal strategy in baseline designs

Answer 15

ABA(B) = reversal strategy. You expect to “recover” the original baseline (A) after the treatment (B).

Data from the baseline and treatment conditions are compared for statistically significant differences.

If you run more than one subject (small-n design), you can provide inter-subject replication&raquo_space;> external validity. Typically 3 to 6 subjects.

Question 16

typical issues with baseline designs

Answer 16

Stability criterion

Uncontrolled variability or variation

Irreversible baselines.

Question 17

what is the stability criterion

Answer 17

choice is “subjective” or based on previous research / pilot study.

• Removes “transitional” data (unless relevant).
• Fixed time or trials: Give a time-limit to reach crit

Question 18

what is uncontrolled variability or variation

Answer 18

unstable, drifting baselines. Caused by extraneous variables

Question 19

what are contrast approaches according to bordens and abbott

Answer 19

“The group approach assumes that if experimental controls fail to reduce uncontrolled variation, then statistical methods should be used to control it. The single-subject approach assumes that if experimental controls fail to reduce uncontrolled variation, then one should endeavour to identify extraneous variables responsible for it and bring them under experimental control.” (Bordens and Abbott, 2008, page 355).

Question 20

types of replication

Answer 20

exact or direct replication

systemic replication

Question 21

what is exact or direct replication

Answer 21

part of the single-subject procedures

Question 22

what is systematic replication

Answer 22

above and beyond that procedure

Question 23

problems with baselines

Answer 23

drifting baselines

unrecoverable baselines

unequal baselines between subjects

inappropriate baseline levels

Question 24

what are drifting baselines

Answer 24

slow, systematic changes

Question 25

what are unrecoverable baselines

Answer 25

reversal does not work due to carryover effects

Question 26

what are unequal baselines between subjects

Answer 26

individual differences in baseline levels

Question 27

what are inappropriate baseline levels

Answer 27

Low baseline good unless data has a floor effect, or high baseline good unless data has a ceiling effect.

Question 28

what are some single subject baseline designs

Answer 28

single factor designs

multifactor designs

multiple-baselines designs

Question 29

what are single factor designs

Answer 29

Single independent variable. AB (necessary if irreversible changes are present), ABA or ABAB designs

Question 30

what are multifactor designs

Answer 30

Two or more independent variables. E.g., melatonin + bright light

Question 31

what are multiple-baselines designs

Answer 31

Several dependent variables. E.g., polygraph.

Question 32

what are dynamic designs and why are they good

Answer 32

Transitional processes and behaviours are crucial and measured.

Excellent to measure behavioural/process dynamics.

Useful also for continuous variations of the independent variable.

The dependent variable is typically continuous.

These designs are often called “time series” designs.

Question 33

examples of dynamic designs

Answer 33

Handwriting behaviour and stress/anxiety
* IV: stress condition, then non-stress condition

Galvanic skin response and stress/anxiety
* IV: questions, sequentially presented

Question 34

what are discrete trial designs

Answer 34

Subjects receive each treatment conditions many times (dozens,
hundreds of times) = trial = datum (one data point).

Extraneous variables are strictly controlled.

Randomized or counterbalanced presentation of treatments (conditions).

Inter-subject variation is often analyzed: comparisons between subjects.

Question 35

what is sequential analysis

Answer 35

Also called “sequential hypothesis testing”.

The sample size is not fixed in advance: sequential estimation is used.

Data are evaluated as they are collected.

Sampling is stopped in accordance with a pre-defined stopping rule as soon as significant results are observed and/or a quota “N” is attained

Question 36

Advantages of sequential analysis and when is it useful

Answer 36

Advantage: Potentially economical (subjects, time, money), but also seeking to attain a “n” that could lead to statistical significance.
*Conclusion can be reached earlier than with common hypothesis testing principles.

Often used in clinical trials (biomedical research).

Useful if subject availability is a concern.

Compromise between idiographic and nomothetic research

Question 37

Procedure: Let’s assume 2 completely randomized (independent group) trials:

If n subjects in each group are available, an interim analysis is conducted on the 2n subjects.

A statistical analysis is performed to compare the two groups, and if the alternative hypothesis is accepted (i.e., the groups are different), the trial is
terminated

what happens if the alternative hypothesis is not accepted

Answer 37

Otherwise, the trial continues for another 2n subjects, with n subjects per group. The statistical analysis is performed again on the 4n subjects. If the alternative hypothesis is accepted, then the trial is terminated. Otherwise, it continues with period evaluation until N of the 2n subjects are available.