How would this misclassification affect the estimate of the causal effect of statin on mortality?

There are 6 questions to be answered after reading an article. It’s about epidemiologic study designs.

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Reading the article in the following website and answer the six questions below:
http://aulafarmacologica.com/wp-content/uploads/2012/11/Las-Estatinas-Reducen-la-Mortalidad-por-C{0e601fc7fe3603dc36f9ca2f49ef4cd268b5950ef1bbcf1f795cc00e94cdd119}C3{0e601fc7fe3603dc36f9ca2f49ef4cd268b5950ef1bbcf1f795cc00e94cdd119}A1ncer-2012.pdfhttp://aulafarmacologica.com/wp-content/uploads/2012/11/Las-Estatinas-Reducen-la-Mortalidad-por-C{0e601fc7fe3603dc36f9ca2f49ef4cd268b5950ef1bbcf1f795cc00e94cdd119}C3{0e601fc7fe3603dc36f9ca2f49ef4cd268b5950ef1bbcf1f795cc00e94cdd119}A1ncer-2012.pdf
1. Statin use information was obtained from prescriptions filled at Danish pharmacies. However, no information was available on whether individuals took the medicine they were prescribed. Could this lead to exposure misclassification / measurement error? Would the error be differential or non-differential? Independent from the outcome or dependent? How would this misclassification affect the estimate of the causal effect of statin on mortality?
2. Page 1794, second column. The authors describe that, in addition to the main analysis including all individuals with cancer, they also performed a matched analysis, selecting 3 non-statin users for each statin user matched for sex, age at cancer diagnosis, year of diagnosis, and cancer type. Did this matching increase exchangeability between statin users and never users? Explain your answer using the information provided in Table 1.
3. In page 1796, first column, Statistical analysis. “Multivariable Cox models were adjusted for age, …, and size of residential area”. What is the purpose of adjusting for these variables?
4. Briefly explain whether the following conditions for identifiability of effects are achieved and how (e.g. in the study design, in the analysis; and if in the design or in the analysis, how exactly, etc.):
a. Positivity ;
b. Consistency ;
c. Exchangeability .
5. The Figure in page 1800 presents results for different stratified analysis. Using the information in the figure, describe the association between statin use and mortality by presence of ‘chemotherapy’. Would your qualitative assessment of the interacion have been different if instead of hazard ratios the figure had used rate…

 

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