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    Module 11 Case Study .

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    Amna Elayan
    Researchers conducted a cohort study of 600 infants in Coffeeville, NY to examine the relationship between maternal smoking during pregnancy and adolescent obesity. They followed the subjects to age 17 and recorded obesity status. Of the original 600 subjects, 450 provided obesity data. The study results were presented in a 2x2 table. According to local data, 11% of 17 year olds in Coffeeville are obese. The researchers used a z-test to determine if the proportion of obese children in the study differed significantly from the Coffeeville population. The z-statistic was calculated to be 3.39, which exceeds the critical value of 1.96. Therefore, the null hypothesis that the proportion is equal to 11% was rejected.

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    Module 11 Case Study .

    Uploaded by

    Amna Elayan
    69 views4 pages
    Researchers conducted a cohort study of 600 infants in Coffeeville, NY to examine the relationship between maternal smoking during pregnancy and adolescent obesity. They followed the subjects to age 17 and recorded obesity status. Of the original 600 subjects, 450 provided obesity data. The study results were presented in a 2x2 table. According to local data, 11% of 17 year olds in Coffeeville are obese. The researchers used a z-test to determine if the proportion of obese children in the study differed significantly from the Coffeeville population. The z-statistic was calculated to be 3.39, which exceeds the critical value of 1.96. Therefore, the null hypothesis that the proportion is equal to 11% was rejected.

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    Researchers conducted a cohort study of 600 infants in Coffeeville, NY to examine the relationship between maternal smoking during pregnancy and adolescent obesity. They followed the subjects to age 17 and recorded obesity status. Of the original 600 subjects, 450 provided obesity data. The study results were presented in a 2x2 table. According to local data, 11% of 17 year olds in Coffeeville are obese. The researchers used a z-test to determine if the proportion of obese children in the study differed significantly from the Coffeeville population. The z-statistic was calculated to be 3.39, which exceeds the critical value of 1.96. Therefore, the null hypothesis that the proportion is equal to 11% was rejected.

    Copyright:

    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd
    Download as pdf or txt
    69 views4 pages

    Module 11 Case Study .

    Uploaded by

    Amna Elayan
    Researchers conducted a cohort study of 600 infants in Coffeeville, NY to examine the relationship between maternal smoking during pregnancy and adolescent obesity. They followed the subjects to age 17 and recorded obesity status. Of the original 600 subjects, 450 provided obesity data. The study results were presented in a 2x2 table. According to local data, 11% of 17 year olds in Coffeeville are obese. The researchers used a z-test to determine if the proportion of obese children in the study differed significantly from the Coffeeville population. The z-statistic was calculated to be 3.39, which exceeds the critical value of 1.96. Therefore, the null hypothesis that the proportion is equal to 11% was rejected.

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    Class Activity

    Common Statistical Tests in Epidemiology


    Part I
    Researchers at the University of Coffeeville in NYC performed a cohort study to investigate the relationship
    between maternal smoking in pregnancy and adolescent obesity. To ensure that the study population was
    representative of the Coffeeville population, they randomly selected 600 infants at birth across Coffeeville.
    Subjects were followed to age 17 to determine if smoking status of the mother during pregnancy is
    associated with obesity status at age 17. Several subjects were lost to follow-up resulting in only 450 teens
    contributing obesity data at the close of the study. The classifications are presented in the 2x2 table below.

    Maternal Smoking Obesity Status at age 17


    Status During Obese Non-Obese Total
    Pregnancy
    Smoked 23 75 98
    throughout
    Never Smoked 49 303 352
    Total 72 378 450

    According to data from the CDC’s Youth Risk Behavior Surveillance System (YRBSS), the prevalence of
    obesity among 17 years olds in Coffeeville is 11%. Using the z-test for a single proportion, test whether the
    proportion of obese children in this study differs from that of the Coffeeville population of 17 year old teens.
    Test at the 5% level of significance. [Use the 7-step hypothesis testing procedure].

    a) Using correct statistical notation, state the appropriate null and alternative hypotheses.

    b) State the rejection region at the 5% alpha level i.e. determine the decision rule.

    c) Compute the value of your test statistic. Test statistics: 0.05/ square root (0.0979/450)= 3.39

    Page 1 of 4
    d) Sketch the appropriate curve to aid in your decision to reject or fail to reject the null hypothesis.

    The critical value =+/- 1.96.

    e) Do you reject or fail to reject the null hypothesis? Why or why not?

    Since 3.39> 1.96, we reject the null hypothesis. There is evidence to conclude the
    proportion of obese children in this study differs from the Coffeville population

    f) State your practical conclusion.

    g) Report the p-value

    h) Construct a 95% CI for the sample proportion. Interpret this interval for your research colleagues.

    i) Your principal investigator asks you to write a draft of the conclusion of your study. What will you
    write (if anything) about the difference in the prevalence of obesity in your sample population vs.
    the Coffeeville population of 17 year old teens?

    Page 2 of 4
    Question 2
    Suppose you measure the resting heart rates (beats per minute) in a sample of “overweight” (defined as
    BMI > 25) and “normal weight” (defined as BMI between 18.5 and 25) men at a state university. There are
    25 overweight men and 20 normal weight men in the sample. Is there a significant difference in the resting
    heart rates of the two groups?

    Resting Heart Rates


    (Beats per minute)
    Overweight Normal
    78 72
    100 82
    100 64
    88 64
    62 84
    94 61
    61 68
    88 69
    78 78
    76 80
    77 87
    90 58
    96 96
    85 68
    83 66
    82 62
    67 72
    77 64
    79 76
    91 95
    80
    75
    75
    68
    90

    a) Using correct statistical notation, state the appropriate null and alternative hypotheses
    Significant difference in resting heartbeats if the two groups

    Page 3 of 4
    b) State the rejection region at the 5% alpha level i.e. determine the decision rule.
    c) Compute the value of your test statistic.

    Where, µoverweight =81.60, Soverweight = 10.74, µnormal =73.30, Snormal = 11.10


    N1= 10.7355
    N2= 11.1029

    The test statistics; 2.53


    The degrees of freedom =40

    d) Sketch the appropriate curve to aid in your decision to reject or fail to reject the null hypothesis.

    The p value is 0.0155. P value is less than 0.05. So we reject the null
    hypothesis. There is evidence to say the significant difference in resting heart
    beats of the two groups

    e) Do you reject or fail to reject the null hypothesis? Why or why not?

    f) State your practical conclusion.

    g) Report the p-value

    h) Construct a 95% CI for the sample proportion. Interpret this interval.

    Page 4 of 4

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