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Escitalopram for treating social anxiety disorder: ‘p’ values can mislead.
- Manjiri Lele, Adhiraj Joglekar (MRCPsych) Specialist Registrar, Child & Adolescent Psychiatry, Windmill Lodge, West London Mental Health NHS Trust, Southall, UB1 3EU (8 April 2005)
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Manjiri Lele, Senior House Officer Regional Secure Unit, West London Mental Health NHS Trust, Southall, UB1 3EU E, Adhiraj Joglekar (MRCPsych) Specialist Registrar, Child & Adolescent Psychiatry, Windmill Lodge, West London Mental Health NHS Trust, Southall, UB1 3EU
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lelemanjiri{at}hotmail.com Manjiri Lele, et al.
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We noted the findings of Kasper et al (2005) and their conclusion that ‘Escitalopram was efficacious in treatment of social anxiety disorder’ with interest. They reported a difference of 7.3 (p=0.005) on Liebowitz Social Anxiety Scale (LSAS) in change from baseline to week 12, favouring Escitalopram over placebo. Kasper et al (2005) suggested this difference was comparable with three previous studies that reported efficacy of Paroxetine in treatment of social anxiety disorder (Stein et al, 1998; Allugander, 1999; Baldwin et al, 1999). Unfortunately without the confidence interval (CI), reliable interpretation of the above difference is not possible. Hence we calculated the standardised effect size, this was 0.22 (CI: 0.01 – 0.43). Though the lower limit of the CI is not reassuring, by convention, the point estimate of 0.22 can be interpreted as ‘small’. We appreciate that small effect sizes can be clinically relevant, especially if the condition treated is common, the putative treatment is - easily available, cheap and without adverse effects. In addition, the given treatment must perform better than other options. We compared the above effect size with the effect sizes for three studies quoted above. The latter were 0.83 (0.53-1.13), 1.36 (0.90-1.80) and 0.38 (0.14-0.61) respectively. Further we looked at the Numbers needed to treat (NNT) based on the responders as per Clinical Global Impression – Improvement (CGI-I) scores. The NNT (CI) for Kasper et al (2005) is 7 (4-20) and that for the comparative studies is 4 (3-6), 2 (2-3) and 3 (3-4) respectively. It’s also important to note that meta-analysis findings on effectiveness of serotonin reuptake inhibitors (SSRI) efficacy in treatment of social anxiety disorder were reported by van der Linden et al (2000). They found a collective NNT of 4 (responders on CGI-I) and a mean effect size for all SSRI of 1.0 (SSRI-placebo difference at end-point on LSAS). None of the 10 SSRI studies included in the meta-analysis reported on Escitalopram. It is tempting to suggest that the placebo response in the Kasper et al (2005) study was high and distorts results. However, if randomisation is presumed to have been successful, an equivalent amount of placebo effect would have occurred in the Escitalopram group. The impressive ‘p’ values reported by Kasper et al (2005) are likely to be due to their study being over-powered and them using analysis of covariance (ANCOVA) which is known to have greater statistical power. Based on our analysis, it is apparent that amongst the different SSRI medications, Escitalopram is less likely to be effective in treatment of social anxiety disorder. We suggest that ‘p’ values can mislead and should not be interpreted as measures of magnitude of effect. References: Allugander, C. (1999) Paroxetine in social anxiety disorder: a randomized placebo-controlled study. Acta Psychiatrica Scandinavica, 100, 193 -198. Baldwin, D., Bobes, J., Stein, D. J., et al (1999) Paroxetine in social phobia/social anxiety disorder. Randomised, double-blind, placebo- controlled study. Paroxetine Study Group. British Journal of Psychiatry, 175, 120 -126 Stein, M. B., Liebowitz, M. R., Lydiard, R. B., et al (1998) Paroxetine treatment of generalised social phobia (social anxiety disorder) - a randomised controlled trial. JAMA, 26, 707 -713. Siegfried Kasper, Dan J. Stein, Henrik Loft, and Rico Nil (2005) Escitalopram in the treatment of social anxiety disorder: Randomised, placebo-controlled, flexible-dosage study. British Journal of Psychiatry 186: 222-226 van der Linden GJ, Stein DJ, van Balkom AJ (2000) The efficacy of the selective serotonin reuptake inhibitors for social anxiety disorder (social phobia): a meta-analysis of randomized controlled trials. International Clinical Psychopharmacology. Supplement 2:S15-23. Declaration of interest: None |
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