Cht. 14 – Single Subject Research
single-subject designs – adaptation of the basic time-series design where data
are collected and analyzed for only one subject at a time
- used to study changes in behavior an individual exhibits after exposure to an
intervention or treatment of some sort
- developed primarily in special ed.
- Primarily use line graphs to present data
o Vertical (ordinate or y-axis) Axis – dependent variable (outcome)
o Horizontal (abscissa or x-axis) Axis – indicates sequence of time
 1.5-2X as long as vertical axis
- description of conditions listed above graph
o first condition is baseline, followed by intervention (indep. Var)
o condition line indicates when condition has changed
- figure caption fives summary; includes indep and dep variables
(see labeled graph, p 300)
A-B Design – collect data on same subject; operating as his or her own control,
under two conditions or phases
- Baseline period
o Subject assessed for several sessions until it seems that typical
behavior has been reliably determined
o Best estimate of what would have occurred if intervention were not
applied
o One should collect minimum or three data points before…
- Intervention condition
o Highly specific behavior tends to be taught w instructor acting as data
collector
- Problems
o Behavior change may not be bc of treatment
o Fails to control for various threats to internal validity
 Does not determine effect of indep variable on dep variable
while ruling out possible effects of extra variables
A-B-A Design – adds another baseline to see if behavir during treatment period
differs from behavior during either baseline period; if it does, effectiveness of
intervention has stronger support
- Problem
o Ethical – involves leaving subjects in A condition
A-B-A-B Design – two baseline periods, two treatment periods; permits
effectiveness of treatment to be displayed twice; second treatment can be
extended indefinitely (p 302). IF behavior is essentially same during both
treatment phases and better or worse than both baselines, another variable
causing change is decreased. Ethical problem avoided
- To do it…
o Reinstate “b” for five dats after second baseline and observe if
dependent variable changes whenever independent variable is applied
Problems – data-collector bias is possible; need for extensive # of data
collection periods (instrumentation effect)
B-A-B Design – if behavior is so severe or disturbing that researcher can’t wait
to est a baseline or if there is a lack of behavior
A-B-C-B Design – c is variation of intervention in B to control for extra attention
the subject may have received during B (p 304)
Multiple-baseline Designs – used when impssible or unethical to withdraw
treatment and return to baseline condition. Collect data on several behaviors for
one subject, obtaining a baseline for each during the same period of time.
- systematically apply treatment @ different times fir each behavior until all
undergo treatment.
o Treatment judged to be cause of change if behavior changes in each
case after treatment has been applied
 More behaviors reduced or eliminated, the more effective the
treatment
 # f times of application depends on subjects involved, setting
and behaviors researcher wants to mess with
o Behaviors being treated remain indep of each other
- sometimes used to collect data on several subjects for a single behavior or
measure a subject’s behavior in 2 or more different settings
- Problems – data points show more fluctuation (trends less clear), collector
bias
Threats to Internal Validity in Single-Subject Research
- Condition Length – number of data points gathered during a condition.
Researcher must have at least 3 points to est clear pattern or trend. Often
difficult to obtain enough data points to see a clear trend ; often are practical
problems (i.e., need to begin study or ethical concern like exhibits dangerous
behavior. Stability of data points must be taken into account by those
who conduct and those who read these types of studies (p 306)
- # of variables changd when moving from one condition to another –
only one variable should be changed at a time when moving from one
variable to another to avoid confounding treatment and yielding erroneous
conclusions
- Degree and Speed of Change – magnitude of when the indep variable is
introduced or removed can lead to degree and speed of change. (for last
three conditions, see graphs p. 308-9)
- Return to Baseline – in returning to the baseline condition, we expect that
the behavior of the subject would return to baseline levels fairly quicly if
intervention had been causal factor in changing subject’s behavior. If this
does not happen, then one or more extra variables may have been the
causal factor that changed subject’s behavior. I it does not return to original
baseline level, extra variables may have produced effects observed during
intervention period. If change is abrupt and rapid, it suggests that indep
variable likely caused changes in dependent variable. If intent is for lasting
impact, we wish for a slower return to baseline level (see graphs p 310)
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Independence of Behaviors – for multiple baseline studies, if researcher
defines two separate behaviors to measure, and both behaviors improve
quickly and considerably, two skills do not seem to be independent – seem to
be dependent on same underlying ability and then improve together
Number of Baselines – the greater the # of baselines, the greater the
probability that intervention is cause of any changes in behavior. PROBLEM
with baselines – the more baselines, the longer later behaviors are kept from
receiving intervention. Takes a long time for behavior to be kept from
receiving baselines. However, the fewer the number of baselines, the less we
can conclude that it is intervention that causes the change in behavior.
Control of Threats to Internal Validity in Single Subject Research
o Most effective in controlling for subject characteristics, mortality,
testing, history threats
o Less effective with location (minor threat – constant throughout), data
collector characteristics (only problematic if data collector is changed),
maturation and regression threats
o Weak in terms of instrument decay, data collector bias (both have
strong likelihood b/c data collected by observations over many trials,
and data collector needs to be told what it is about), attitudinal and
implementation threats (both are not well controlled b/c can
unintentionally distort results)
 Data collector bias – problematic when same person is
implementer and data collector (i.e., teacher)
 Second observer reduces this threat but increases
amount of staff needed
Weak when it comes to external validity – generalizability – must rely on
replications across individuals rather than groups to make them worthy
Multi-treatment design introduces different treatment into ABAB (AVACA)
Alternating Treatments Design – alternates two or more different
treatments after initial baseline period
Multiprobe design – fewer data points used than multiple-baseline design
to resuce datas collection burden and threats to internal validity
Features of all of these designs can be combined.
The final pages of the chapter was an example of Single-Subject Research that
was published at some point, and the authors of the text analyzed the research in
terms of topics discussed in this chapter and in chapter 13. To be honest, the
content of the study was confusing. It was concerning whether or not the
oversimplification hypothesis was actually true (people will be more likely to
behave a certain way if given a reward, and when the reward is taken away, they
will be less likely to continue the behavior… i.e., if you play guitar @ first because
you like it, and then you got paid for it, you will not want to do it for as long
without getting paid at the same time). They tested this little boy Arnold who is
mentally retarded, autistic and visually impaired who bangs his head and is
institutionalized by creating a baseline sorting silverware (an earlier indep.
Activity) then added the B by letting him play with fun toys of his choice (all for
timed intervals) if he performed the original indep action. They found the opposite
to be true of the oversimplification hypothesis. See pp. 312-322 for a sample of a
real live scientific research report with commentary!
Then, on pp. 323-324, they review every section that was done to say whether it
was done well or if it needed improvement. None of this was mentioned in the
final chapter review, so now I am wondering if I totally just wasted my time…