chapter 13 research in depth: longitudinal and single-case studies

Chapter 13Research In Depth:

Longitudinal and Single-Case Studies

Longitudinal Research• Longitudinal Research: A design in which an

investigator studies the same people or the same population (but different individuals) over time, sometimes across decades

• Cross-Sectional Research: A design in which an investigator studies groups of different people who vary on some characteristic (e.g., age) at the same time.– Cohort Effects: In longitudinal research, differences in

people resulting from characteristics of the era or social environment in which they grew up rather than to age effects specifically. This is a potential problem in cross-sectional research.

Longitudinal Research

Common Themes in Differences in Participants in Longitudinal Research

Genetic differences that underlie behavior. Genetics may underlie 25% of the variability in cognitive abilities, but much less for personality characteristics (Schaie, 2000)

Environmental differences that affect behavior. Changes in the social context, including cohort effects, may change behavior.

Interaction between genes and environment. Genetic effects may unfold because of environmental influences such that genetically-influenced behaviors will differ greatly in different environments.

• Trend Studies: Longitudinal research in which an investigator samples randomly from a population over time, with different individuals constituting each sample

Varieties of Longitudinal Research

The Issue• How widespread is youth suicide?• It is a significant issues, particularly in some

ethnic groups.

Example: Trends Over TimeQuestion: • How many students have suicide ideation in

the state of Vermont? What is the pattern over time.

Method: In a trend study, Vermont studied middle- and

high-school students regarding their thoughts of suicide since 1995.

• Results: Over 20% of students claimed to have made a plan for suicide in 1995, but the number declined over the next decade to just over 10%. There was also a decline in the number of students who required medical treatment.

Example: Trends Over Time

Example: Trends Over Time

Results of Vermont trend study on suicidal ideation

Example: Trends Over TimeConclusion• A troublesome number of students think of

suicide, although the percentage declined between 1995 and 2005.

• It would be wise for the state to think about interventions to prevent suicides.

Cohort Study: • A type of longitudinal research in which an

investigator randomly samples from a population selected on the basis of specific characteristics.– The Nurses Health Study began in 1976 as a

simple questionnaire study.– The NHS now involves about 122,000 nurses and

collects data on lifestyle and diseases, and it includes samples like blood and tumor tissues.


Cohort-Sequential Samples• A type of longitudinal research in which an

investigator repeated measures a cohort group (e.g., people 60 years of age) over time, adding a new cohort (e.g., new 60-year olds) in each wave in order to differentiate age effects and cohort effects.


• Question: When children begin using alcohol, does their consumption increase over time?

• Method: In a cohort-sequential design, investigate the alcohol intake of different age groups, following a group of 6th grade, 7th grade, and 8th grade children over three years.



• Result: Among children using alcohol, as they get older, their alcohol use increases in similar ways.

• Conclusion: When children use alcohol early (e.g., in the sixth grade), their consumption increases in consistent ways.

Results of cohort-sequential study on alcohol use in children


Source: Bray, J. H., Adams, G. J., Getz, J. G., &Baer, P. E. (2001). Developmental, family, and ethnic influences on adolescent alcohol usage: A growth curve approach. Journal of Family Psychology, 15 301-314. Copyright © 2001 by the American Psychological Association. Adapted with permission.

Varieties of Longitudinal ResearchPanel Studies• A type of longitudinal research in which an

investigator studies the same individuals over time.– The most famous panel study is Lewis Terman’s

study of gifted children that began in the 1920s and continues today, although the few people still alive are quite old.

– A more typical example involved a study of bullying that lasted one year, with data collected in three waves (Bond et al., 2001)

• The National Assessment of Educational Progress (NAEP) has investigated student performance in different subjects for over three decades

• Examination of reading, math, and science scores, results suggest that compared to the 1970s, today’s students score comparably or better much of the time, although scores have fluctuated over the years.

Controversy: Student Achievement

NAEP Results

• In math and reading, students scored at least as well in 2008 as they had in 2004 or in 1971 when the measurement began.

Controversy: Student Achievement

Issues in Longitudinal ResearchLongitudinal Approaches

Type of Study Comment

Retrospective Study--An approach to studying change over time that relies on people’s memory and recollections of the past.

This may be the only viable approach to studying the effects of a traumatic event that occurred in the past.

Prospective Study–An approach to studying change over time that identifies research participants at the beginning of the project who are followed throughout the course of research.

This approach is viable when a researcher can begin a study at some critical time and is able to follow people forward in time from the event.

Attrition• The loss of participants in longitudinal research

due to death, disappearance, loss of interest, etc.– Attrition is one of the most serious methodological

problems associated with longitudinal research.– Those who drop out might differ in important ways

from those who remain, so conclusions based on studies with significant attrition can be suspect.

Issues in Longitudinal Research

• Attrition can make conclusions ambiguous– Bond et al. (2001) studied bullying and found that

(a) boys had a greater attrition rate than girls and (b) boys showed a lower incidence of depression associated with bullying.

– Could it be that boys who were depressed dropped out of the study? Or could it be that boys do not get as depressed due to bullying as girls do?

– Because of attrition, it is not clear what is happening with boys who are bullied.


Sometimes attrition may not make a difference– LaGreca et al. (1996) studied students who had

suffered greatly due to Hurricane Andrew.– The attrition rate was 22% over ten months, which is

a typical rate for this kind of study.– The researchers compared those who left the study

with those who remained. There were no differences with respect to grade, gender, ethnicity, or initial symptoms of PTSD.

– The researchers concluded, based on the participants who remained in the study, that the data are likely to be valid and representative of the population.


Reasons for attrition in the Hurricane Andrew study of PTSD.



Wutzke et al. (2000) reported that they were able to maintain contact with about three quarters of their sample of heavy drinkers over 10 years, a remarkable statistic for their population, which is notable for very high levels of attrition.

Steps Taken to Reduce Attrition in a Longitudinal Study of Heavy Drinkers

Preparation

Ensure accuracy in verifying dates of birth and middle names to make later tracking easier

Identify a contact person who lives at a different address

Maintain contact throughout the project with such mailings as birthday cards or regular newsletters

Persistence

Begin a trace of the person as soon as contact is lost

Make multiple phone calls to set up appointments for interviews

Show willingness to conduct interviews at times and locations convenient for the respondent

Provide incentives to offset the inconvenience of participation

Experimental Analysis of Behavior• An approach typically involving one or only a

few individuals– Measurements tend to be highly objective and

quantitative

Single-Subject Experimentation

Methods of Single-Case DesignsTypes of Withdrawal Studies Involving Presentation, Then

Withdrawal, of a Treatment

Note: A = No treatment (or withdrawal of treatment)B = Application of treatment

ABA Design–Type of design in which researchers get a baseline measurement of behavior (A), apply some treatment (B), then withdraw it (A).

ABAB Design–Type of design in which researchers get a baseline measurement of behavior (A), apply a treatment (B), withdraw the treatment (A), then re-apply the treatment (B)

Multiple Baseline Design–Type of design that studies multiple behaviors that may change across baseline, treatment, and withdrawal phases

Single-Subject Randomized Controlled Trials (RCT)

• A research design involving the study of a single person over multiple trials, with trials involving application of the treatment and trials with no treatment occurring in random order.– Also called an N of 1 randomized clinical trial

• This approach is often used in applied, clinical settings.

Methods of Single-Case Designs

Methods of Single-Case DesignsNecessary Criteria for Appropriate Use of Single-Case

DesignsThe behavior or condition being studied must be chronic and stable.

The treatment (e.g., a drug) should have a rapid effect and rapid cessation of effect when withdrawn.

There needs to be a clear and objective outcome that can be measured reliably (Cook, 1996).

• Question: Will application of drugs help restore concentration in a brain-injured patient?

• Method: In an N of 1 RCT, administer a placebo, lorazepam, or dextroamphetamine sulfate on randomly selected days. [Placebo on day 2, lorazepam on days 1 and 4, and dextroamphetamine sulfate on days 3 and 5 with a day in between to eliminate carryover effects of the drugs]

Example of Single-Case Design

Example of Single-Case Design

• Result: Performance was better with dextroamphetamine sulfate than with the other two treatments.

• Conclusion: One of the drugs outperformed the other drug and the placebo.


Strengths of Single-Participant Designs

These designs provide extensive, rich detail about the behavior of the person being studied.

These designs are highly appropriate for studying rare people or rare conditions.

Results of single-case designs are good for generating further research hypotheses and experiments.

Results of single-case designs can provide useful plans for treatment and therapy.


Weaknesses of Single-Participant Designs

There are questions of external validity: Will the results generalize to other people?

There are questions of internal validity: There are concerns over conclusions of causation if there is no manipulation of an independent variable.

Misunderstanding About Single-Case Research

Most psychological research involves groups, so psychologists are not familiar with the strengths of single-case designs.

Researchers may confuse the objective, controlled, and quantitative single-subject experiments with more qualitative and subjective case studies.

Some researchers are concerned that single-case studies have low internal and external validity, even though many of the same concerns hold true for research using groups.

Some researchers claim that single-case research is too subjective, as when investigators study internal, emotional states, even though the same concerns would hold for group research.


• Case Study: A research design involving the in-depth study of one or a few people, traditionally with no manipulation of variables.– Case studies are descriptive in nature and

generally do not lead to valid causal conclusions.– Case studies can be useful for preliminary

research of rare cases.• When AIDS first appeared, there were few cases, so

researchers relied on case studies.

Case Studies

A Synesthete• A man remarked that the chicken he was cooking

was not done because it was too round and did not have enough points, that angel food cake has a pink smell, and that quinine (a bitter liquid) felt like polished wood.

A Case Study: Tasting Pointed Chickens and Seeing Colored Numbers

A Case Study: Tasting Pointed Chickens and Seeing Colored Numbers

– The man was a synesthete who experienced a stimulus with multiple senses (synesthesia).

– Synesthetes are rare, so they can only be studied in single-case designs and case studies.

– Cytowic (1993) studied this man for two years, demonstrating that when experiencing synesthesia, there was minimal blood flow to the cortex and maximal blood flow to the limbic system.

– Because the extensive study involved a single person, it is not clear that every synesthete’s brain acts similarly.

chapter 13 research in depth: longitudinal and single-case studies

Documents

time slide

type of longitudinal

cohort effects

cohort study

time question

suicidal ideation slide

age effects

time conclusion