Sampling and Confidence Intervals
For this Discussion, you reflect on the poll described in the Week 4 Introduction. In this poll, the margin of error is 5 percent and the point estimate is 65%, therefore you can add and subtract the margin of error (5%) to the point estimate (65%) and state, based on this sample, you are 95% confident that the actual percent of Americans who prefer bottled water is a range somewhere between 60% and 70%.
Usually this confidence is expressed at the 95% level, but it does not have to be. If you wanted a narrower range, for example. If you wanted to say that that the percentage of Americans who prefer bottled water is between 62% to 67%, you might need to use a lower confidence interval, say 90%, instead of 95%. On the other hand, if you wanted to state you were 99% confident in your estimate, your range might need a wider confidence interval for your estimate, perhaps 55% to 75%.
To prepare for this Discussion, review this week’s introduction, your readings, and the above discussion. Then, read the description of a study, located in the initial Week 4 Discussion area and consider how you could explain the results through your knowledge of sampling and confidence intervals.
Write a brief summary of the study described above. Then, describe how you would use your knowledge of sampling and confidence intervals to explain the results of the study to a coworker with no knowledge of statistics. Finally, explain the importance of confidence intervals to public health research.
Prevalence of Asthma in the United States in 2009
Asthma is a serious chronic disorder that affects the respiratory capacity of children and adults. Asthma can manifest itself with shortness of breath, acute chest tightness or pain, and excessive coughing and wheezing. The proper management of asthma is essential to improving quality of life and reducing health costs. Public Health professionals need access to current data on the prevalence of asthma in their communities to insure that those with asthma have access to effective care and treatment. The National Health Interview Survey (NHIS) is conducted by telephone annually on a carefully stratified random sample of U.S. children and adults.
The NHIS collected data on the prevalence of asthma in the U.S in 2009. Table 1 includes the prevalence and 95% confidence intervals of asthma among children and adults by sex, race/ethnicity, poverty, and region. (CDC, 2011) For the Week 4 Discussion in your online classroom, you can choose which characteristic’s prevalence to describe to a co-worker. Be sure to explain what the 95% confidence interval means and how a sample of 38,815 can be used to estimate prevalence for all of the United States.
Characteristic Children <18 yrs Adults = 18 yrs
No. in Sample % 95% CI No. in Sample % 95% CI
Total (Asthma) 11,129 9.6 8.9-10.4 27,686 (7.7) (7.3–8.1)
Male 5,640 (11.3) (10.2–12.5) 12,241 (5.5) (5.0–6.1)
Female 5,489 (7.9) (7.0–8.9) 15,445 (9.7) (9.1–10.3)
White, non-Hispanic 4,816 (8.5) (7.6–9.5) 16,099 (8.1) (7.6–8.6)
Black , non-Hispanic 1,791 (17.0) (14.5–19.9) 4,347 (8.7) (7.5–10.1)
Hispanic 3,420 (7.7) (6.5–9.2) 5,159 (5.5) (4.7–6.4)
Other Race 1,102 (9.6 ) (7.5–12.2) 2,081 (6.6) (5.3–8.4)
Poverty threshold (Based on Federal Poverty Level)
Poor 2,307 (13.5 ) (11.6–15.5) 4,591 (10.6) (9.5–11.7)
Near Poor 2,595 (9.5 ) (7.9–11.3) 5,698 (8.1) (7.3–9.1)
Not Poor 6,227 (8.3) (7.5–9.1) 17,397 (7.0) (6.6–7.6)
Northeast 1,828 (11.1) (9.5–13.0) 4,598 (8.7) (7.8–9.9)
Midwest 2,289 (10.9 ) (9.2–12.8) 6,239 (8.1) (7.3–9.0)
South 4,024 (9.8 ) (8.7–11.0) 10,139 (6.8) (6.2–7.4)
West 2,988 (7.1) (6.0–8.5) 6,710 (7.9) (7.0–8.8)
CDC. (2011). Vital signs: asthma prevalence, disease characteristics, and self-management education — United States, 2001–2009. MMWR. Morbidity and Mortality Weekly Report, 60(17), 547-552. Retrieved from http://www.cdc.gov/mmwr/preview/mmwrhtml/mm6017a4.htm?s_cid=mm6017a4_w#tab1