07章_实验流行病学解说.pptVIP

* 1.相对稳定（失访问题），足够数量（样本量） 2.发病率（样本量、统计效力） 3.近期没有流行（否则自然产生抗体） 4.较好的医疗卫生条件（实施：医务工作者素质高、配合好，质量有保证；实施过程中出现任何不良反应，也可以较好应对） * 1.对干预措施有效的人群：即可能发生所研究的结局的人(疫苗－传染病：易感人群) 2.预期发病率较高的人群：出于对所需样本量大小的考虑 3.干预对其无害的人群：老年人、儿童、孕妇、哺乳期妇女，已知药物对其有不良影响的人（有胃刺激的药不能用于有胃出血史的人） 4.能将实验坚持到底的人群：癌症、严重肾、肝病者，这些人可能在研究尚未结束前就死亡或因病重而被迫停止试验 5.依从性好的人群 入选标准、排除标准 排除： * 干预措施实施前、后的变化越大，所需样本量越小：既可以是计数资料、也可以是连续资料 干预前结局指标越高，所需样本量越小：如果想模拟这个变化，切记固定的前后大小，应该是相对大小，而不是绝对大小。例如，干预前后率为40%和30%，即两者变化10%，为40%的1/4，则当干预前的率升高为50%时，两者的变化值不应是40%，而是50%-50%*1/4=37.5% * 仅适用于实验性研究 能控制已知和未知的混杂因素 在样本量较小的研究中，由于机会的作用，随机化过程可能并不能完全平衡两组的混杂因素；样本量越大，这个问题越小 但是不能消除混杂! * 系统随机分组：身份证号码、病例号、学号… 样本量小的时候，有时难以达到平衡 样本量大的时候，较容易达到平衡 * 组间非处理因素可比：配比、随机分配 组间效应测量可比：客观测量工具或方法保持一致，主管一致性（盲法） * In health care research, however, bias is defined as any factor or process that tends to deviate the results or conclusions of a trial systematically away from the truth.3-6 This deviation from the truth can result in underestimation or exaggeration of the effects of an intervention. biases that can occur at any point during the course of a trial, from the allocation of participants to study groups, through the delivery of interventions and the measurement of outcomes, to the interpretation and reporting of results. Other types of bias that tend to receive less attention can also, however, have a profound influence on the way in which the results of RCTs are interpreted and used. These biases can occur during the dissemination of a trial from the investigators to potential users, or during the uptake of trial information by potential users of the trial. * A perfectly randomised method to allocate participants to the study groups does not, however, protect an RCT from selection bias. Selection bias can be introduced if some potentially eligible individuals are selectively excluded from the study because of prior knowledge of the group to which they would be allocated if they participated in the study. Imagine that the investigator in charge of recruiting patients f