In the analysis, the investigators decided to focus on the soil, air, and blood Mn levels for
exposure measurements, and to focus on hand-cye coordination (by Pursuit Aiming Test) and
motor coordination (by Luria Test) for outcome measurements They considered age, gender,
SES and study site as potential confounders.
Q1. Summarize the distribution of measured exposure (soil, air. blood Mn), outcome scores
(total correct dots from Pursuit Aiming Test and Luria score), as well as other relevant
characteristics (age, gender, SES. study site, obesity) in Table Note that the lab technician
labeled any soil Mn level >1200 Oppm as lab error and should be removed from analysis
Hint: For continuous variables, report mean and SD if normally distributed, and report median
and 25th/75th percentiles if not normally distributed For categorical variable, report
number of observations and percentage
In addition to Table 1. answer the following questions:
1a) Are the exposure measurements and outcome measurements normally distributed?
Which of them are skewed and what is the direction of skewness?
1b) For exposure measurements that are not normally distributed does log transformation
help with normalizing the data? Assess by histograms, Q-Q plots, and normality tests.
Q2. Examine the associations between Mn exposure and motor function outcomes, using
univariate linear regression and multivariate linear regression adjusting for age, gender, SES. and
study site. Consider treating the exposure as both continuous (log transformation only if needed)
and quartiles. Summarize the quantitative results in Table (for Pursuit Aiming Test) and
Table (for Luria Test). See sample table on Page 5
Hint: When treating the exposure variable as continuous, researchers sometimes still proceed to
evaluate the associations using parametric methods (such as linear regression) even if the
distribution of predictors is not completely normal after data transformation (but within
reasonable acceptable range based on other alternative criteria). For this assignment, please
proceed the analysis even when log -transformation does not fully help with normalizing the data
Table (Insert title)
Blood Mn As continuous**
Multivariate analysis adjusted for age, gender, SES. and study site.
** Hint: Please note whether the variable was in original scale or log --Transformed scale.
Q3. Summarize your interpretation of the results in Table 2 and Table 3 above:
3a) Write Results section as seen in journal articles which summarizes the observed
quantitative results If the results are similar for univariate analysis (crude association)
and multivariate analysis (adjusted association), focus on multivariate analysis results
For models treating exposure variable as continuous, interpret the associations by
each 1-unit increase for original scale, and by 10% increase for log- transformedscale.
For models treating exposure variable as quartiles, discuss whether the results
suggest exposure- response relationship (whether the change in outcome becomes
larger as exposure becomes higher)
3b) Write abrief Conclusion paragraph within 3 sentences: as seen in the last part of the
Abstract in journal articles. What is the main message you learned from these results?
Q4. Based on your findings from Questions 1-3, answer the following questions.
4a) Were the association with motor function outcomes consistent when considering soil
Mn and air Mn? If not, explain why you think the results may be different. (Hint:
think about whether there is: possibility of exposure misclassification and how would
this affect the observed associations, what is the timing of exposure that each
measured exposure metric reflects, etc.)
4b) In addition to age, gender, SES, and study site that were adjusted in the analysis, the
investigators have also considered other factors as potential confounders of the
association between Mn exposure and motor function. These include: (i) experience of
playing video games, (ii) occupation that requires hand dexterity, and (iii) alcohol
consumption. Do you think these are possible confounders? Ifso, explain what the
direction of confounding and why If not, explain your reason.
Q5. The investigators were also interested in examining whether obesity may modify the
association between Mn exposure and motor function measurements. Table 4is the results of
obesity-stratified analysis that the investigators reported for soil Mn and Pursuit Airning Test
Table 4. Association between soil Mn (log -transformed) and number of correct dots in Pursuit Aiming
Test: stratified by obesity status
a Multivariate analysis adjusted for age, gender, SES. and study site
Based on Table do you think there is suggestion of effect modification by obesity on the association
between soil Mn and hand-ey coordination? Explain why or why not. and state your conclusion
Q6. Replicate the analysis in Table 4,but looking at Luria Test score as the outcome instead of
Pursuit Aiming Test. Summarize these results in Table (using the same format as Table 4) and
briefly discuss the findings.
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