流行病学通常被称为公共卫生的“基石”，它是一门研究疾病的分布和决定因素，健康状况，或人群间的活动和应用于控制健康问题的学科。由于流行病学与现实生活息息相关，并更好地评估公共卫生项目和政策，学生将理解流行病学的研究方法，通过这一门课所学到的理论知识应用到当今的公共健康问题。本课程通过流行病学的视框，探讨了心血管疾病和传染病等公共卫生问题，对地区情况和全球情况都进行了讨论。 翻译: Yi Zhou

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来自 The University of North Carolina at Chapel Hill 的课程

流行病学：基础公共卫生科学

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流行病学通常被称为公共卫生的“基石”，它是一门研究疾病的分布和决定因素，健康状况，或人群间的活动和应用于控制健康问题的学科。由于流行病学与现实生活息息相关，并更好地评估公共卫生项目和政策，学生将理解流行病学的研究方法，通过这一门课所学到的理论知识应用到当今的公共健康问题。本课程通过流行病学的视框，探讨了心血管疾病和传染病等公共卫生问题，对地区情况和全球情况都进行了讨论。 翻译: Yi Zhou

从本节课中

Understanding Measures of Disease Frequency

This module introduces measures of disease frequency.

- Dr. Karin YeattsClinical Associate Professor

Department of Epidemiology, UNC Gillings School of Global Public Health - Dr. Lorraine AlexanderClinical Associate Professor, Director of Distance Learning (North Carolina Institute for Public Health)

Department of Epidemiology, UNC Gillings School of Global Public Health

[NOISE] In this lecture, we are going to cover the definition of risk.

An important thing to remember about a risk is that it's

a probability of getting either a disease or a health outcome.

And that it's for a population and not an individual.

[MUSIC]

[BLANK_AUDIO]

The learning objectives for this segment are as follows.

Define and calculate the measure of risk.

Choose the measure of risk for the appropriate situation

and interpret risk within the context of public health research.

But, let's first note risk is a common word with a broader meaning.

For this course we will have a very specific definition.

The numerator for

a risk are incident or new cases.

These are new cases that are identified during the study follow up.

The denominator is the study population at risk of getting

the disease or health outcome at the beginning of follow-up.

So the formula looks like this.

It's number of incident or new cases

divided by the total number of at-risk individuals.

Risk measures the number of new or incident cases of the health outcome

that develop among people in the population

at risk over a specified time period.

Risk refers to the probability that a health outcome will occur.

Risk can be expressed as a proportion, and ranges from zero to 100%.

You may be wondering why we use the risk as a measure.

We use risk as a measure

for several reasons.

First, it's fairly easy to calculate and interpret.

It also has clear meaning to clinicians

and lay-people, and patients understand basic percentages.

So let's go through an example.

Risk can be used to make various health

decisions both at a population and individual level.

At an individual level risk can be used to help

patients decide whether to accept a drug intervention.

Note there's a caveat that this risk estimate is

not specifically for that individual but for a population.

For example, Alendronate medication. A specific inhibitor of osteo class

mediated bone re-absorption, can increase bone mineral density, or BMD and prevent

radio-graphically defined vertebral fractures.

This figure is from a study that examined radio-graphs

of women who received Alendronate versus a placebo group.

The figure shows the risk of hip fractures in placebo and treatment groups over time.

It shows new cases of hip fractures

developing during the 36 month time period.

In the three year study, fractures of the hip occurred in 22 or 2.2% percent of 1005

patients on the placebo, and 11, or 1.1% of 1,022

patients on the alendronate sodium, which is commonly known as Fosamax.

The figure displays the risk of hip fractures in this study.

When calculating

risk, we generally assume that the entire population at risk at the beginning of

the study period has been followed to

determine who develops the health outcome of interest.

A closed study population means no new individuals

are entering the study once the study has started.

So no individuals could join halfway through the study for example.

In a closed study population, people in the study do not leave or

enter the population due to birth, death, migration, loss to follow up, etcetera.

Next we will discuss how a risk is actually calculated.

In order to calculate risk we must define

our study population, or the population at risk.

And then we determine the number of incidents

or new cases of the health outcome or disease.

Next, we specify

the time period.

So this is what the formula looks like.

Risk is the number of new cases of the health outcome

divided by the population at risk during a specified time period.

So let's try an example calculation. Here we have 11,000 people that were in an

area around a large nuclear power plant. And they were followed for 7 years.

Or until the development of any cancer of the blood.

30 cases were identified over the 7 year period.

What is the risk of developing the outcome of interest?

So in this case, we take the numerator as 30 new cases,

and we divided by the population at risk which is given to us as 11,000.

Then we calculate the risk as 0.0027

or 0.27%. Then we can convert this

to a more easily understood statistic. By multiplying by

1,000 so then the risk is interpreted as 2.7

people per one 1,000 over a 7 year time period.

So next we'll have a short in-video quiz

so you can try calculating a risk yourself.

This concludes our segment on risk which

included both the definition, showed you some calculation

and also an example of how to, how is risk is used in the population.