
Epidemiology Sampling & Confidence Intervals
Author:
Dr.Janet ForresterProfessor
Tufts University School of Medicine
USA
Access: 
1.1 An introduction to the human body Read Online
1.2 The chemical level of organization Read Online
After studying this chapter, you will be able to:
Though you may approach a course in anatomy and physiology strictly as a requirement for your field of study, the knowledge you gain in this course will serve you well in many aspects of your life. An understanding of anatomy and physiology is not only fundamental to any career in the health professions, but it can also benefit your own health. Familiarity with the human body can help you make healthful choices and prompt you to take appropriate action when signs of illness arise. Your knowledge in this field will help you understand news about nutrition, medications, medical devices, and procedures and help you understand genetic or infectious diseases. At some point, everyone will have a problem with some aspect of his or her body and your knowledge can help you to be a better parent, spouse, partner, friend, colleague, or caregiver.
This chapter begins with an overview of anatomy and physiology and a preview of the body regions and functions. It then covers the characteristics of life and how the body works to maintain stable conditions. It introduces a set of standard terms for body structures and for planes and positions in the body that will serve as a foundation for more comprehensive information covered later in the text. It ends with examples of medical imaging used to see inside the living body.
Lect 10: Epidemiology & Biostatistics Sampling and Confidence Intervals
We will teach you how to read and critique medical journal articles using examples from some of the most widelyread medical journals. To critique the medical literature you will need to understand the fundamentals of epidemiologic study design, the sources of bias, and the role of chance. Every discipline has its own jargon. we will cover the terminology used in clinical research, including the basic statistical jargon. The most important concepts are in the lectures and small groups provide you with an opportunity to apply what you have learned from the lecture material to actual medical journal articles.
As future physicians you have an obligation to remain current in your field of practice and to treat patients according to generally accepted standards of care.
Question: Use the following information for questions 13: In a cohort study of breast cancer in older women, there are two groups, those who were exposed to a known carcinogen and those who were not.
Choices:
First, find the standard error: = Standard deviation / sqrt(N) = 12 / sqrt(196) = 12/14 = 0.857 Then, calculate the confidence intervals: 95% CI = mean + 1.96*SE = 105 + 1.96*0.857 = 105 + 1.68 = (103.3, 106.7)
Question: Must the standard error always be at smaller than the standard deviation if there is more than one person in the group of interest? Why or why not?
Choices:
Yes, because the standard error is a function of the standard deviation. As long as the sample size is greater than 1, the standard error will always be smaller than the standard deviation.
Question: Use the following information for questions 13: In a cohort study of breast cancer in older women, there are two groups, those who were exposed to a known carcinogen and those who were not.
Choices:
Standard error = Standard deviation / sqrt(N) = 8 / sqrt(169) = 8/13 = 0.615
Question: Which of the following is a TRUE statement?
Choices:
Confidence intervals are always symmetric.
Confidence intervals for an odds ratio require that the distribution is normal or Gaussian.
For large samples, the distribution of sample means will be approximately normal, regardless of the distribution of the population characteristic.
If group A has a mean of 40, a sample size of 50, and a standard deviation of 10, and if group B has a mean of 40, a sample size of 40, and a standard deviation of 11, then the standard error of Mean A will be larger than the standard error of Mean B.
If group A has a mean of 40, a sample size of 50, and a standard deviation of 10, and if group B has a mean of 42, a sample size of 50, and a standard deviation of 10, then the standard error of Mean A will be larger than the standard error of Mean B.
Question: Interpret the 95% confidence interval for mean number pounds of corn consumed by a sample of cows at an industrial feedlot of a beef farm: (10.7, 21.4)
Choices:
We are 95% certain that the true sample mean pound of corn consumed by cows is between 10.7 and 21.4.
We are 95% certain that the true population mean pounds of corn consumed by cows is between 10.7 and 21.4.
We are 95% certain that between 10.7 and 21.4 pounds of corn will be fed, on average, to an individual cow.
Ninetyfive percent of the cows in the sample consumed between 10.7 and 21.4 pounds of corn.
Question: Use the following information for questions 13: In a cohort study of breast cancer in older women, there are two groups, those who were exposed to a known carcinogen and those who were not.
Choices:
The width of the confidence interval will decrease, since the denominator, sqrt (N), increases
Question: How does increasing the sample size affect the power of the study?
Choices:
Increasing the sample size increases the power of the study. In the notes, you’ll see that studies with large sample sizes have high power to detect effects or differences. We’ll talk more about this in the following lecture.