Hi my name is Michelle Bankhead Subject: Epidemiology Please provide a detailed
ID: 166363 • Letter: H
Question
Hi my name is Michelle Bankhead
Subject: Epidemiology
Please provide a detailed explanation with all calculations at your earliest conveinence.
Thanks !!!!!
Data Interpretation and Confounding
Epidoria Birth Weight Study
Background – In the small island nation of Epidoria, a team of reproductive epidemiologists has been studying the relationship between very low birth weight and risk of cognitive, motor, and behavioral problems. Five years ago these investigators initiated a study. Using birth certificate files and delivery room entry logs, these investigators attempted to identify all full-term births in Epidoria over a 6-month period. The investigators enrolled all low birth weight babies and a representative sample of normal birth weight babies into their study. The investigators then examined the children every year until age 3 years. During the last examination, the investigators administered a standardized developmental screening test to assess personal-social, language, and motor-adaptive skills. Based on this test, the investigators classified the children into two groups: normal development and delayed development.
The results from the study were:
Development
Delayed
Normal
Total
Birth Weight
Low
140
220
360
Normal
77
283
360
Total
217
503
720
Background (cont.) – To account for the possibility that environmental lead exposure might confound the relationship between birth weight and developmental status, blood lead levels were determined from blood samples collected at the age 3-year visit. Elevated lead levels (> 10 micrograms/ dL) were found in 173 of the low birth weight children (88 of whom had delayed development according to their screening test). Elevated lead levels were also found in 72 of the normal birth weight children (24 of whom had delayed development).
c) Carry out a stratified analysis of birth weight and developmental delay, controlling for blood lead level. Create 2x2 tables for each stratum of lead level and estimate the relative risk for each stratum.
d) Comparing the findings from the crude and stratified analysis, is there a suggestion of confounding by lead exposure in this example?
e) Is there evidence of an association between blood lead level and the primary exposure variable in this study (hint create a 2x2 table for blood lead level and exposure)?
f) Is there evidence of an association between blood lead level and the outcome in this study?
g) Based on all of this information would you judge blood lead level to be a confounder of the association between birth weight and delayed development? Explain your answer.
Development
Delayed
Normal
Total
Birth Weight
Low
140
220
360
Normal
77
283
360
Total
217
503
720
Explanation / Answer
Ans- Elevated lead levels (> 10 micrograms/ dL)
Birth weight (High Lead)
CIR = 1.53
Development lead levels (<10 micrograms/ dL)
Birth weight (Low Lead)
CIR = 1.51
WE can see the the crude CIR is sronger than the stratum-specific CIR's.however in compare between low birth weight and delayed birth weight remains even after controlling the elevated blood lead.
ans- Birth weight
Prevalence ratio = (173 x 360) / (72 x 360) = 2.4
From the table it is clear that there is an association between blood lead level and low birth weight (the primary exposure); low birth weight children are substantially more likely (prevalence ratio 2.4) to have elevated blood lead levels.
(Note that the OR = (173 x 288) / (72 x 187) = 3.7 means that the odds of an elevated blood level are 3.7 times as high for low birth weight babies,which is not equivalent to "3.7 times as likely". In this case the outcome elevated blood lead level) is not "rare", so odds and proportions are different from each other, as are their respective ratios.)
ans- For this situation we look into the normal bith weight group.
CIR = (24/72) / (53/235) = 1.81
DEVELOPMENT LOW NORMAL TOTAL DELAYED 88 24 112 NORMAL 85 48 133 TOTAL 173 72 245 CI 88/173 24/72 0.506 0.33Related Questions
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