Cross-Sectional and Longitudinal Studies

In Paper 2 Clinical, it is important that you make the methods relate to clinical examples. You need to think carefully about why these methods are particularly useful when doing research in clinical psychology.

Before we get into this, let’s remind ourselves of what is meant by cross-sectional studies.

Describe what is meant by a cross sectional study (3)

  • A cross sectional study takes one moment in time and compares one group of participants with another group of participant at that time.
  • Participants are only tested once and the findings provide a snapshot of the differences between the behaviour of the two groups tested. It is therefore similar to an independent measures design.
  • Cross sectional studies are often used to look at the effect of age as an independent variable on certain key behaviours or abilities. For example, you might compare 3 year olds and 6 year olds with regard to the amount of aggressive behaviours shown towards their same sex parents.

Example of CS study in clinical psychology:

Hyde et al (1994): Cognitive decline and schizophrenia: Patients with chronic schizophrenia, aged from 18 to 69 years were divided into five cohorts: 18-29, 30-39, 40-49, 50-59 and 60-69 (five levels of the IV) and intellectual deterioration was tested using the Mini-Mental State Examination and the Dementia Rating Scale plus other tests known to be sensitive to cognitive impairment in progressive dementia (the DVs). The Pps had passed a rigorous screen for any co-morbid condition that might be affecting their CNS function. There was no evidence of accelerated intellectual decline. Performance on the Boston Naming Test significantly declined with age, this was mainly due to age rather than duration of illness. Mean test performances were abnormal across all age groups but intellectual function does not seem to markedly decline during the adulthood of patients with schizophrenia.

Describe what is meant by a longitudinal study (3)

  • A longitudinal study assesses the same group of participants repeatedly over an extended period that is usually several months or even years.
  • This allows the researcher t look at how behaviour/performance changes over time and developmental trends can be established.
  • In a way it is similar to a repeated measures design where age is the independent variable.
  • If you wanted to research how children relate differently to their same sex and opposite sex parents in order to research Freud’s Oedipus Complex, you could observe the same group of children several time, e.g. at age 3, 4, 5, 6 and 7, (by which point they should have moved out of the phallic stage) and see whether levels of aggression shown towards the same sex parents decreases over time.

Activity: Think about Hyde’s cross-sectional study; how would cognitive decline in schizophrenia be assessed in a longitudinal study? What problems would Hyde et al have encountered if they had done the study longitudinally? What advantages might this approach have had?

Example of a longitudinal study on the same topic, cognitive decline in people with schizophrenia: Harvey et al (1999)Cognitive decline in late-life schizophrenia: a longitudinal study of geriatric chronically hospitalized patients.

The study looked at 326 geriatric, chronic, long-stay schizophrenic patients. The patients showed cognitive and functional impairments that were in decline, post illness-onset. The study lasted 30 months and there were two separate assessments of the patients. Cognitive and functional impairments (the DV) was measured using the Clinical Dementia Rating (CDR). Of those Pps who had less severe scores at the start of the study (baseline), 30% had declined further by the second assessment and only 7% of the sample with lower scores at baseline appeared to improve in their functioning. Several characteristics of the patients at baseline assessment predicted increased risk for cognitive and functional decline, including lower levels of education, older age, and more severe positive symptoms.

Activity: Compare Harvey et al and Hyde et al; what strengths are there in Harvey’s study which are not present in that of Hyde and vice versa?


You need to be able to compare cross sectional and longitudinal studies. Make sure you have practiced this! Always use examples such as Hyde et al and Harvey et al in your writing.

Technique tips: When you see the word compare, think: similarities and differences. State a point about one of the things you are asked to compare and then say how the other is similar in one way but different in another. Do this as many times as you can in the time allowed. Remember the ‘Venn Diagram’ can be a helpful way to plan your answer.

Content tips:

  • one moment of time/over a period of time
  • same group of people/different groups of people
  • Pps assessed once/Pps assessed repeatedly
  • developmental trends
  • change over time
  • cost
  • practicality
  • drop out rate and bias
  • recruitment of Pps
  • ethics
  • follow ups
  • control
  • generalisability

Useful connectives: whereas, in contrast, on the other hand, similarly, but, yet, alternatively, nevertheless, both

A very useful concept for evaluation: Cohort Effects

The cohort are the group of people being studied. Cohort effects refers to factors relating to this group which might make them special in some way and thus not entirely comparable to another similar group who might be selected in years to come in a replication of the study. These factors cannot be controlled and therefore could become a confounding variable. Classic cohort effects relate to things which happened only to that specific generation of children, e.g.

  • Children who have lived through a world war; the impact of war is something that cannot be replicated in a future study and therefore the influence of living through a war becomes an example of a cohort effect
  • Children who have been subjected to certain educational initiatives which have subsequently gone out of fashion; the outcomes of these initiatives cannot be replicated in the future and become a cohort effect
  • Economic recession can affect a cohort in a way which cannot be replicated in future years; the effects of recession on the original children is an example of a cohort effect.

When you conduct a cross sectional study, each of the group of children may have lived through differing social and economic circumstances and these will not necessarily be the same meaning that you cannot be sure that any differences between the children’s performance/behaviour is due to differences in their age or differing experiences of each cohort. This is a problem for cross sectional studies.

In longitudinal studies cohort effects can affect the generalisability of the results. It is possible that the finding and conclusions will only apply to groups of people who have lived through similar social and economic circumstances to the original group of participants.

cross-and-long-models: A handout containing the text above.

Make your own top trumps cards:



In Paper 3, you might be asked about cross sectional and longitudinal studies in general. Of course you may use your examples from clinical to help illustrate your answers however, it is also useful to practice some questions with non-clinical examples.

Practice Questions

(a) Seif is an educational psychologist who is interested in researching whether students perform better if they have one examination at the end of a two-year course or if students perform better if they have several examinations throughout the two years of the course. Seif has decided to carry out a longitudinal study to compare the two approaches to student examinations. Describe how Seif may carry out his longitudinal study. (7)

You may wish to include some of the following:

  • Method
  • Variables
  • Apparatus
  • Sampling
  • Ethics

(b) Evaluate the longitudinal research method, as it is used in psychology. (4)

Charles is carrying out an experiment on young children. He wants to see if there is a difference between 4 year olds and 8 year olds in their ability to understand that a tall, narrow glass of water can hold the same amount of water as a short, wide glass. Charles had two short, wide glasses that held the same amount of water. The children watched him pour one of these glasses of water into a tall, narrow glass. Charles then asked the children if the short, wide glass and the tall, narrow glass had the same amount of water in them.

(a) Identify the independent variable (IV) in this experiment. (1)

(b) Identify the dependent variable (DV) in this experiment. (1)


(i) Identify the experimental design Charles used in this study. (1)

(ii) Outline one strength and one weakness of the experimental design you identified in 12(c)(i). (4)

(d) Describe the ethical issues Charles must consider when carrying out his experiment with the children. (4)