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KMID : 1094020140310040288
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Journal of Veterinary Clinics
2014 Volume.31 No. 4 p.288 ~ p.292
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Sample Size Calculation for Cluster Randomized Trials
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Pak Son-Il
Oh Tae-Ho
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Abstract
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A critical assumption of the standard sample size calculation is that the response (outcome) for an individualpatient is completely independent to that for any other patient. However, this assumption no longer holds when thereis a lack of statistical independence across subjects seen in cluster randomized designs. In this setting, patients withina cluster are more likely to respond in a similar manner; patient outcomes may correlate strongly within clusters. Thus,direct use of standard sample size formulae for cluster design, ignoring the clustering effect, may result in samplesize that are too small, resulting in a study that is under-powered for detecting the desired level of difference betweengroups. This paper revisit worked examples for sample size calculation provided in a previous paper using nomogramto easy to access. Then we present the concept of cluster design illustrated with worked examples, and introduce designeffect that is a factor to inflate the standard sample size estimates. carbohydrate are great production problems for goat in Bangladesh. This study designed to investigate the prevalenceof lactic acidosis and then response to different therapeutic agents. For this purpose, 1,128 goat were examined atoutdoor District Veterinary Hospital, Faridpur, Bangladseh for treatment of which 40 goats were found positive forlactic acidosis showing 3.55% prevalence of disease. The highest occurrence found in female (4.64%) of over 3 yearsage (4.64%) in indigenous goat (2.7%). For therapeutic assessment the forty affected goats were divided into fourgroups A, B, C and D comprising of 10 animals each. Group A were given magnesium hydroxide 8% w/v at 1 g/kg body weight orally. In group B magnesium hydroxide 8% w/v at a dose as group A combination with 7.5% sodiumbicarbonate at the rate of 0.9 ml/Kg body weight intravenously administered. Goat in group D were treated with mixtureof ginger, nuxvomica, sodium carbonate, cobalt sulphate, dried ferrous sulphate and thiamin mononitrate at the rateof 1 g/kg body weight orally. Goat of group C treated with combination drugs of group A, B and D. The rectaltemperature, pulse rate, respiration rate, was performed before and after treatment. It was found that the highest recoveryin group C with an average period of 21 ± 1.8 hours. It was concluded that lactic acidosis is a common disease ofgoats and its severity can be effectively reduced by using combination drugs.
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KEYWORD
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sample size, nomogram, cluster design, design effect
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