(8)流行病学导论-Introduction to Epidemiology-公开课-关爱惟士
(8)流行病学导论-Introduction to Epidemiology

课程视频http://player.youku.com/embed/XMzYwNjcyNjkwNA



Professor Kaarin Anstey

Kaarin Anstey教授


In epidemiology we look at a particular health problem in terms of the population. Whereas clinicians are just focusing on an individual patient, in epidemiology we want to look at the prevalence, so how common is a particular health condition across the entire population, and at what rate does it increase. So we talk about incidence. So if we’re looking at dementia, we’d say, “how many people have dementia at this point in time?” - that’s the “prevalence.” And “over the next five years, how many people would develop dementia?” - that’s the “incidence.” And then another critical aspect of epidemiology for this is looking at “risk factors,” so things that increase the chance that a person will develop the disease that we’re studying.

在流行病学的研究中,我们是从人群水平来了解某一特定的健康问题。临床医生只是专注于个体患者,而在流行病学中,我们是要观察患病率,即在整个人群中特定的健康问题有多严重。另外还要观察它以什么样的速度在增加,所以我们谈论发病率。因此当我们研究认知症的流行病学时,我们会说,“在这个特定时间点有多少认知症患者?” - 这是指“患病率”。而“在接下来的五年中,会有多少人发展成认知症? - 这是指“发病率”。此外流行病学的另一个关键点是观察“风险因素”,就是增加一个人发展我们正在研究的这种疾病的概率。



I’m going to be talking about the types of epidemiology studies that are conducted, to answer questions of prevalence, incidence and risk. So, to get the prevalence of a disease, say dementia, we need to have a sample that we study that is representative of the population. Ideally, for example, in Australia we would take a random sample of the entire population of Australia, but we’ve got such a large land mass here that’s not possible. So we often do a representative sample of a particular region, and then we extrapolate up to the country population from that. So that’s a single, one-off survey that we could do or study. Often we want to do a longitudinal study, especially if we’re looking at risk factors. So we take a cohort and we do a longitudinal study or what’s also called a prospective study, or it’s sometimes called a cohort study. And that’s where we take this group of people who’ve been sampled randomly from a defined area or population, and we follow them over time, and we test the same people again and again and again. And we look at how their risk factors may change and whether or not they develop dementia longitudinally.

我将介绍我们已经进行的不同类型的流行病学研究,以解答有关患病率,发病率和风险方面的问题。因此为了获得例如认知症等疾病的流行情况,我们需要一个代表人群作为我们研究的样本。例如,在澳大利亚,理想状况下是对整个澳大利亚的人口进行随机抽样,但在这么大的土地面积上我们是不可能的这样做的。因此,我们通常在一个特定区域抽取一个有代表性的样本,然后从中推断出整个国家的人口情况。这是一个我们可以做或执行的单一的,一次性的调查研究。特别是如果我们在观察风险因素的话,我们通常会做一个纵向研究。因此,我们采取排队列的方法做纵向研究,或称为前瞻性的研究,或有时称为队列研究。这就是我们从一个定义的区域或人群中随机抽样组成一组人群,我们随访他们,然后一次又一次地调查同一组人群。我们观察他们的风险因素是否变化,以及他们是否会纵向发展成认知症。


How useful is an observational study or an epidemiology study in the field of dementia epidemiology in establishing a risk and causality, compared to a randomised control trial? To answer that question, we actually have to take a step back. And we have to think about the fact that dementia occurs due to pathological changes in the brain, and these occur over decades. So they’re not occurring over a very short period of time like 12 months or two years. And, so, we can’t actually conduct short-term studies on the causes of dementia at the population level; we need to have that long-term information to see who’s going to go and develop dementia. From that point of view, we’re really left with cohort studies as the main method of studying risk for dementia.

与随机对照试验相比,认知症的观察性流行病学研究能够为风险和因果关系的建立起多大作用呢?要回答这个问题,我们实际上必须后退一步。并且我们必须考虑痴呆发生是由于大脑了发生了几十年的病理变化的这一事实。因此,他们不会发生在一个像12个月或两年这样非常短的时间。因此,我们实际上不能在人群水平上对认知症的原因进行短期研究;我们需要有这些长期的信息来观察谁会患上和发展认知症。从这个角度来看,我们确实应该将队列研究作为研究痴呆风险的主要方法。


And, secondly, a number of the risk factors that have come out from the research that’s been conducted are things that we couldn’t examine using a randomised control trial methodology. I’d just better explain what a randomised control trial is. A randomised control trial is when you take a sample and you randomly allocate the members of the study to different conditions, and then because of the randomisation, you’re able to adjust for all of the potential factors that may influence the results. So, for example, you might conduct a randomised control trial of a drug that theoretically is thought to prevent dementia, and every person who came in would get a random allocation to drug, or no drug. The problem is, with dementia, again, it takes so long to develop and the brain changes take a long while to accumulate, so we couldn’t conduct a short-term randomised control trial. And, secondly, it wouldn’t be ethical to look at some of the risk factors for dementia in a randomised control trial. For example, we couldn’t ask people to smoke to see if smoking caused dementia. We couldn’t expose people to heavy air pollution, to see if that causes brain damage that’s irreversible. The sort of questions that you’d end up asking are just almost illogical and they’re completely unethical. So we really can only look at these questions using what we call observational studies, where we look at exposure just through normal life, whether the people chose to smoke, whether they lived in an area with heavy air pollution, and then we use statistical methods to try to adjust for all of those potentially confounding factors. And then we follow people up and see if those what we call “exposures,” so exposure to smoking or air pollution or heart disease of whatever, if those things increased the risk long-term of dementia.

其次,已开展的研究发现一些风险因素是我们无法使用随机对照试验方法研究的。首先我先解释什么是随机对照试验。随机对照试验是当您抽取一个样本并随机分配到不同的组别,然后由于采用了随机分配,你能够控制所有可能影响结果的潜在因素。因此,例如,您可以对理论上被认为能预防认知症的药物进行随机对照试验,并且每个纳入的人都会随机分配到给药组和不给药组。问题是认知症需要很长的时间来发展,而且大脑的变化需要很长时间的积累,所以我们不能进行短期的随机对照试验。其次,在随机对照试验中观察认知症的某些风险因素是不道德的。例如,我们不能要求人们抽烟,看看吸烟是否导致认知症。我们不能让人们遭受严重的空气污染,看看是否会导致不可逆的脑损伤。你最终要问的此类问题时几乎是不合逻辑和不道德的。因此,我们的确只能使用我们所谓的观察性研究来研究这些问题,我们只能通过日常生活状态来观察暴露,从而了解人们是否吸烟,是否居住在空气污染严重的地区,然后使用统计方法来尝试调整所有这些潜在的混杂因素。然后我们跟随这些人群,看看我们所谓的“暴露”,即暴露于吸烟,或空气污染,或者心脏病这些是否能增加认知症的长期风险。


So, the question is: how do we evaluate the results of observational studies that show, for example, factor A is a risk factor, and then a similar study in another country might find it’s not a risk factor? There’s a number of approaches to this problem. This is something that we deal with – well, I in particular in my group, at the Australian National University, deal with a lot. First of all, we look at the quality of the research design of the study that found the result, did they adequately adjust for potential confounders? Was the sample biased? How long did they follow up the sample; is it a long enough follow up? Was there a lot of sample attrition leading to sample bias? Were the measures adequate? Did they properly measure the exposure and did they have a proper measure of dementia diagnosis at outcome? So you look at all of these design issues. Was it a big enough sample to give a statistically robust result?

因此这个问题是:我们如何评估观察性研究的结果,例如,因素A是一个风险因素,而在另一个国家的类似研究可能会发现它不是这样。有很多的方法可以解决这个问题。这是我们,特别是我在澳大利亚国立大学的研究小组,处理很多这样类似的情况。首先,我们看看发现结果的研究设计的质量,他们是否适当调整了潜在的混杂因素?样本是否偏倚?他们随访了样本多久了;随访期是否足够长?失访率是否很高进而导致样本有偏倚?采取的措施是否足够?暴露测量是否恰当,并且认知症作为结果进行诊断是否恰当?所以你要注意所有这些设计要点。是否能提供一个足够大的样本从而给出统计上的可靠的结果?



So that’s the first approach, and sometimes that alone will tell you that the result is probably not reliable, because there are methodological flaws in the study or limitations that mean it’s inconclusive. Secondly, what we do in this field of dementia epidemiology is that we consider each cohort study as one study in a sample of studies, and there’s actually a population of these studies, so we assume there is a true finding of an effect. So we do something called “meta-analysis,” and that’s where we bring together all of the different studies on a particular topic. So if we took, for example, smoking, does smoking increase risk of dementia, we would get all of the published studies on smoking and risk of dementia and we’d use statistical methods to pool the results. And that gives us a robust estimate and we can actually look at something called the study bias, the selection or publication bias using statistical techniques to see if we have got a good representation of all of those studies. And, from that, we derive a much more robust estimate of the effect and a standard error around that estimate, and that’s really what we prefer to use, rather than just the result of a single study.

所以有时单独使用第一种方法--观察性流行病学研究时,由于这种研究存在方法上的缺陷或局限,结果可能不可靠。其次,我们在痴呆流行病学领域所做的是,我们把每个队列研究作为这些研究的一个样本,实际上是这些研究的某一个人群,所以我们假设每一个影响因素会有一个正确的结果。因此,我们做了一个名为“荟萃分析”的工作,也就是我们将某个主题的所有不同研究集中在一起。因此,如果我们以吸烟是否增加得认知症的风险的研究为例,我们将搜集所有关于吸烟和痴呆风险的研究的文章,我们将使用统计学方法来汇总结果。这给了我们一个可靠的估计,并且我们可以考察统计技术使用的所谓的研究偏倚,选择偏倚或发表偏倚来看看我们是否能很好的代表这些研究。因此,我们得出一个更加可靠的效果估计和拥有较小的标准误,这正是我们真正喜欢使用的,而不是仅仅一个单一研究的结果。


翻译:关爱惟士-未经允许不得转载,违者必追究法律责任


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