Read the paper by Jiang et al. (2010) 'Smoking cessation and carotid atherosclerosis: the Guangzhou Biobank Cohort Study -- CVD' and answer the following questions in relation to the given article.

1) What is the research question of this study?

2) What type of study design was used in this study (the actual study type)? Identify two key features of the study type presented in the paper. Indicate the study type that would give the highest quality of evidence for the research question?

3) What is/are the study factor(s)? How did the author measure the factor(s) and classify study groups based on the factor(s)?

4) What is/are the outcome factor(s) and how was the outcome status determined?

5) How were cases identified? Describe the procedures used to ascertain cases.

6) What are the main findings of the study in determining the relationship between the study factor and the outcome factor (See Tables 3 & 4)? (In your answer indicate any association(s)such as RR/OR with 95% CI found in the research)

7) How was the association between the risk factor and outcome factor assessed? Please describe the methods/ statistical techniques used to assess the association.

8) Identify major sources of selection bias in this study. Could selection bias have had any effects on the observed association between the study factor and the outcome factor? Provide reasoning to support your answers

9) Could information bias have affected the results in any way? Why or Why not?

10) How have the authors dealt with the issue of confounding? What are the potential confounders considered by the authors? Could confounding have affected the observed results? Explain your view briefly.

11) Could age have any effect on the association between the study factor and the outcome factor? Explain your view briefly.

12) In Table 4, the authors used various statistical models to compare the risks of CCA atherosclerosis and carotid plaques in different smoking cessation groups with current smokers. Did the results show any changes in risk by years of quitting? Were the results likely to be true effects? Or could the results be explained by chance? Please summarise the overall findings in words.

13) Which of the Bradford Hill's criteria for evaluating causality are more likely to be met in this study? Give one reason for each of your selected criterion to justify your answers.

14) Could the results of this study be generalised to different populations? Explain your reasons briefly.