 We obtained an estimate of the variability of the change in ESRS dyskinesia scores after 12 weeks of treatment with ethyl-EPA and placebo as add-on to their previous antipsychotic medication from a previous trial conducted at our centre, which gave 2.13 as the standard deviation unpublished. Using this estimate and with a significance level of 5 and 90 power, 32 patients per randomised group would be sufficient to detect a 1.75 point difference in change in ESRS dyskinesia scores the difference obtained in our preliminary study from baseline to endpoint. Allowing for an estimated withdrawal rate of 30, we will need to recruit 42 patients per treatment group into this study. 