What you'll learn

• Why the POTS study by March et al. (2004) matters for treating obsessive compulsive disorder in young people.
• How the study compared cognitive behavioural therapy, sertraline, combined treatment and placebo.
• The key findings, including why combination treatment was especially effective.
• How to evaluate the study for AO3: methodology, ethics, validity and real-world usefulness.

First: what is OCD?

Obsessive compulsive disorder, usually shortened to OCD, is a mental health condition involving unwanted intrusive thoughts and repetitive behaviours or mental acts.

For example, a young person might have an obsession that their hands are contaminated, followed by a compulsion to wash repeatedly. The compulsion may reduce anxiety briefly, but this relief can reinforce the behaviour, making OCD harder to break.

Why study treatments for children and adolescents?

OCD often begins in childhood or adolescence. If symptoms are treated early, the person may experience less disruption to school, friendships, family life and later development.

The POTS study is important because it did not just ask whether treatment works. It compared different treatment options in a controlled way.

The treatments compared

Cognitive behavioural therapy

Cognitive behavioural therapy, or CBT, is a psychological therapy based on the idea that thoughts, feelings and behaviours are linked. For OCD, CBT often includes exposure and response prevention.

So, if a child fears contamination, ERP might involve touching a “contaminated” object and then delaying or avoiding handwashing. The aim is to learn that anxiety naturally falls without the compulsion.

Sertraline

Sertraline is a drug treatment from a class of antidepressants called selective serotonin reuptake inhibitors, or SSRIs.

SSRIs are used for depression, anxiety disorders and OCD. In OCD, they may reduce the intensity of obsessive thoughts and compulsive urges.

Combined treatment

Combined treatment means using CBT and sertraline together. The logic is that medication may reduce symptoms enough for the young person to engage more successfully with CBT, while CBT teaches long-term coping skills.

Aim of March et al. (2004)

The POTS team, including March et al. (2004), aimed to compare the effectiveness of:

• CBT alone
• sertraline alone
• CBT and sertraline combined
• pill placebo

The study was titled “Cognitive behaviour therapy, sertraline, and their combination for children and adolescents with OCD.”

Method: how the study was designed

March et al. used a randomised controlled trial, often shortened to RCT.

The sample included 112 children and adolescents aged 7 to 17 with a primary diagnosis of OCD. They were randomly allocated to one of four treatment groups for 12 weeks. Each group had 28 participants.

The four conditions

1. CBT alone: therapy focused on OCD symptoms, including ERP.
2. Sertraline alone: medication treatment.
3. Combined CBT and sertraline: both treatments together.
4. Pill placebo: an inactive pill used as a comparison condition.

Measuring improvement

The researchers used standard clinical measures, including the Children’s Yale-Brown Obsessive Compulsive Scale, usually called CY-BOCS.

The study also used clinical improvement ratings, and assessments were carried out by evaluators who were masked to treatment condition.

Results: what did they find?

All three active treatments improved OCD symptoms more than placebo. The strongest outcome was for combined CBT and sertraline.

Clinical remission rates were approximately:

• Combined treatment: 53.6%
• CBT alone: 39.3%
• Sertraline alone: 21.4%
• Placebo: 3.6%

This suggests that both psychological and biological treatments can help childhood OCD, but using them together may produce the greatest short-term improvement.

Conclusion

March et al. concluded that children and adolescents with OCD should be offered CBT, sertraline, or especially their combination where appropriate. The findings support a biopsychological approach, because OCD can be treated through both psychological learning processes and biological intervention.

AO3 evaluation: strengths

Strong experimental control

A major strength is that this was a randomised controlled trial. Random allocation reduces the chance that one group was more severe, more motivated or more likely to improve before treatment even began.

The placebo condition also helped researchers judge whether improvement was due to active treatment rather than expectation.

Use of standardised measures

The CY-BOCS is a well-established measure of OCD severity. This improves reliability, meaning the assessment can be applied consistently across participants.

Real-world application

The findings have clear practical value. They support treatment guidelines recommending CBT with ERP and SSRIs for young people with OCD, especially when symptoms are moderate to severe.

This is useful for clinicians, families and schools because it gives evidence-based guidance on treatment planning.

AO3 evaluation: weaknesses and issues

Limited generalisability

The participants were children and adolescents who met the study criteria and were treated in specialist clinical settings. This means the findings may not generalise perfectly to adults, very young children, people with complex comorbid conditions, or those treated in less specialist services.

CBT cannot be fully blinded

Medication and placebo can be double-blinded more easily, because participants may not know whether they are receiving the real drug. However, CBT cannot be hidden in the same way: participants know whether they are attending therapy.

This could create expectancy effects. For example, a family receiving CBT may expect improvement, which might influence motivation or symptom reporting.

Short treatment period

The trial lasted 12 weeks. This is useful for measuring short-term treatment response, but OCD is often long-lasting. Longer follow-up is needed to know whether improvements are maintained, whether relapse occurs, and whether young people continue using CBT strategies.

Possible side effects and adherence

Sertraline can have side effects, and not all young people want to take medication. Some may also struggle to complete ERP tasks because exposure can be distressing at first.

Ethics

Because participants were children and adolescents, ethical safeguards were especially important.

Using the BPS Code of Ethics and Conduct (2009) as a framework, key issues include:

• Consent: parents or guardians would need to give informed consent, and young people should give assent where possible.
• Right to withdraw: families should be able to leave the study without penalty.
• Protection from harm: side effects, distress during ERP and symptom deterioration must be monitored.
• Confidentiality: clinical information should be stored securely and anonymised where possible.
• Debrief: participants and families should be informed about the treatment and study findings when appropriate.
• Deception: the placebo condition involves some withholding of full information, so it must be justified by scientific value and managed carefully.

Research methods link: analysing this kind of study

For A-Level exam answers, you may be asked to connect the study to research methods.

If you were analysing simplified POTS-style data:

• Use measures of central tendency such as the mean or median for symptom scores.
• Use measures of dispersion such as the range or standard deviation to show spread.
• Use a bar chart for remission rates across treatment groups.
• Use a histogram to inspect whether symptom scores are normally distributed or skewed.
• Use a frequency table for categories such as “remitted” and “not remitted”.

For inferential testing:

• Mann-Whitney U: difference between two independent groups, such as CBT versus placebo, especially if scores are ordinal or skewed.
• Wilcoxon signed-ranks: difference between two related scores, such as before-treatment versus after-treatment scores for the same participants.
• Spearman’s rho: correlation, such as whether higher starting severity is related to poorer improvement.
• Chi-square: association between categories, such as treatment group and remission category.

The usual significance level is $p\le .05$. A stricter level, $p\le .01$, reduces the risk of a Type I error, which is a false positive. A more lenient level, $p\le .10$, may be used in exploratory research but increases the chance of claiming an effect when there is not one.

For critical-value tables, remember the decision rule:

• For Mann-Whitney U and Wilcoxon, the observed value usually needs to be equal to or less than the critical value.
• For Spearman’s rho and chi-square, the observed value usually needs to be equal to or greater than the critical value.

A one-tailed test is used for a directional hypothesis, such as “combined treatment will reduce symptoms more than sertraline alone”. A two-tailed test is used for a non-directional hypothesis, such as “there will be a difference between treatments”.

How to use this study in essays

For AO1, describe the aim, sample, four conditions, 12-week RCT design, measures and findings.

For AO2, apply the findings to treatment decisions. For example, if a child has severe OCD, the study suggests combined CBT and sertraline may be considered, alongside ethical monitoring and family involvement.

For AO3, evaluate the strong control and clinical usefulness, but balance this with issues of generalisability, expectancy effects, placebo ethics and the relatively short follow-up.