Power analyses(samples size calculation)is critical in protocol design for clinical trials.Adequate power ensures the credibility and reliability of the clinical trial results.In this article,omega-3 fatty acid supplementation study is chosen as an example to explain the power analysis in practice during the study design.First,obtaine the parameter estimates from the high-quality literature review and relevant systematic review(meta analyses)results.Then,calculate the sample size under different parameter settings and select the final patient number according to the clinical practice.Based on the above information,statistical simulation is performed to assume diverse possible combination of the outcome in real clinical trial.Further,under the specific determined sample size,the simulation pointing out the different positive or negative results when the real clinical trial is conducted.The determination of sample size of a clinical trial should be based on both the clinical and statistical considerations.

Objective To investigate current status of cognitive behavior on chronic obstructive pulmonary disease (COPD) to provide evidence for targeted intervention.Methods A questionnaire survey on COPD was conducted at 12 settings of 4 prefectures that were sampled from Ningxia Province using multistage stratified cluster random sampling method,and 4268 residents at least 40 years old were interviewed.Multivariate linear regression method was used for data analysis.Results A total of 4056 valid questionnaires were returned from 4200 participants with an effective response rate of 96.57％.Only 6.51％(264/4056) had an idea of COPD,13.88％ (563/4056) regarded cigarette smoking as a risk factor of chronic bronchitis and emphysema,and 6.39％ (259/4056) knew pulmonary function tests.Home income,living area,education level and ethnicity were main factors influencing COPD awareness.The percentage of current cigarette smoking was 28.80％ (1168/4056) with 20.40％ in Hui (Muslim) ethnic group and 34.63％ in Han ethnic group (P ＜ 0.05 ) ; smoking index and severe smokers were not significantly different between the two groups ( P ＞ 0.05 ).Conclusion Our data suggest a considerably poor knowledge and prevention awareness of COPD in Ningxia Province.In spite of relatively lower cigarette smoking rate,the problem that Hui (Muslim) ethnic people are lack of COPD awareness should not to be neglected.

Background Retinopathy of prematurity (ROP) threats the visual function of prematurity patients.The screen of ROP is very important for the early prevention and treatment.Some relevant works have performed in several region and cities in China.But the survey data is still lack in Shandong province.Objective This work was to survey and analyze the screening result of ROP in Jinan city and assess the risk factors for ROP.Methods A cross-sectional study was designed.Two hundreds and eighty-eight eyes of 144 cases with low birth weight or prematurity were clinically examined in Shandong Eye Hospital from June,2008 to June,2010.The screening criteria was established based on the ROP screening guidelines and the outcome implemented by Ministry of Public Health with minor modification,including newborn infants with birth weight of 2500 grams or less and gestational age of 34 weeks or less.The history and systemic status were recorded,and the screening results were compared with those obtained from the national screening criteria.Gestation age and birth weight between the infants with and without ROP were compared using student t-test.The ratios of persistent oxygen inhalation were tested by Fisher' s exact test.Results In all examined infants,30 eyes of 15 cases (10.42％) developed ROP,including 12 eyes of 6 cases suffering from stage Ⅰ,8 eyes of 4 cases from stage Ⅱ,8 eyes of 4 cases from stage Ⅲ with plus disease and 2 eyes of 1 case from stage V.In ROP patients,gestation age ranged from 27 weeks to 33 weeks with the average weeks of 30.85±1.79,and the birth weight ranged from 910 grams to 1980 grams with the average weight (1408.89±259.93)grams.Statistical analysis showed that the gestation age and birth weight in prematurity infants with normal fundus group were (32.38±1.48) weeks ranged from 28 weeks to 35 weeks and (1763.19±338.62) grams ranged from 1310 grams to 2450 grams respectively,showing a shorter gestation age (t=3.71,P＜0.01 ) and a lower birth weight ( t =2.88,P＜0.01 ) in ROP infants.The ratios of persistent oxygen inhalation in normal fundus group and ROP group were 58.91％ and 60.00％,respectively with the insignificant difference between them (P =1.000).Conclusions The incidence of ROP is 10.42％ in the present study,which is consistent with the result from other region in China,suggesting that the national criteria is practical for the ROP screening in Jinan region.Prematurity and low birth weight are identified as the high risk factors of ROP.