Assignment 2 (50 marks in total)

1. (12 marks). Thirty teeth were randomly allocated into three groups of 10 and a cavity in each tooth filled using one of three preparations. Following immersion in a dye, the percentage of linear leakage occurring at the tooth/restoration interface in each tooth was determined. The results are stored in columns of the file data2_Q1.sav in which the first column contains the percentages of length of penetration (PLP) and the second column contains the preparation used.
   1. Produce an analysis of variance (ANOVA) table to determine if there are differences between the preparations using PLP measurement. (2 mark)
   2. Produce Q-Q plots or normality test to assess the validity of the ANOVA assumptions. (2 marks)
   3. For PLP measurements, conduct Bonferroni post-hoc tests to determine where any differences between the preparations lie. (2 marks)
   4. Perform Kruskal-Wallis tests for PLP measurements. What is your conclusion? (2 marks)
   5. Use pairwise Wilcoxon rank-sum tests (with Bonferroni correction) to determine where any differences between preparations lie. (2 marks)
   6. Which analysis do you think is most appropriate here – ANOVA or a nonparametric approach? (2 marks)
2. (8 marks). Researchers at Leeds University School of Dentistry want to know whether registering with a NHS dental practice or a private dental practice will make a difference in children’s regular check-ups. Consider the table of data collected:

1. What is the proportion of children that have registered with NHS dental practice? (1 marks)
2. What is the proportion of children that have registered with private dental practice? (1 marks)
3. What is the proportion of children that have registered with NHS dental practice in the group of regular check-ups? (1 marks)
4. What is the proportion of children that have registered with private dental practice in the group of regular check-ups? (1 marks)
5. What is the absolute difference in the proportions of that have registered with NHS dental practice in the group of regular check-ups, compared to the group of non-regular check-ups. (1 marks)
6. Conduct a chi-square test with null hypothesis that there is no association between dental practice and regular check-ups. What is your conclusion? (3 marks)

1. (5 marks). A study considered the effect of diet control over caries development in children. Of 30 children, 15 were randomly selected to receive controlled diet over 5 years (cases), and the other 15 formed a control group. Eight of the 15 in control group developed caries during this 5-year period, while one of the 15 children developed caries in the study group. The data are stored in the file data2_Q3.sav .
   1. Should we use chi-square test or Fisher’s exact test? Why? (2 marks)
   2. Use Fisher’s exact test to determine whether the results were significantly better for study group than control group. What is your result? (3 marks)
2. (3 marks). A study identified 47 patients in need of two fillings. Subjects were then treated with one filling using material A and the other filling with material B. In order to compare the success rate between material A and B over two years, the data are collected and stored in the file data2_Q4 . sav and shown in the contingency table below.

1. Use McNemar’s test to determine if the proportion of success with material A is the same as material B in this matched-pairs study. Comment on your results. (3 marks)

1. (8 marks). The data file data2_Q5.sav contains information on the percentage of people who brush their teeth at least once a day and the percentage of people who have caries for a range of developed and developing countries.
   1. Produce a scatter plot of teeth-brush rate against percentage of caries and comment on the results. (2 marks)
   2. Calculate Pearson’s correlation coefficient for these data. Test whether the correlation coefficient is significantly different from zero. (2 marks)
   3. Calculate Spearman’s rank correlation coefficient for these data. Test whether the correlation coefficient is significantly different from zero. (2 marks)
   4. Which of the two correlation coefficients do you think is a more appropriate summary of the relationship between the variables and why? (2 marks)
2. (9 marks). A study discussed the relationship between cigarette smoking and the mortality index for mouth cancer in men. The subjects were residents of 16 regions of Great Britain, Norway, and Sweden. The objective of the study was to determine whether a linear relationship between the variables was appropriate. The data are given in the file data2_Q6.sav .
   1. Construct a scatter plot of mouth cancer mortality index against cigarette smoking amount. (3 marks)
   2. Fit a regression line with the smoking amount as the independent variable and mortality index as the dependent variable. (3 marks)
   3. Add the regression line to your plot and interpret your results. (3 marks)
3. (5 marks). Reflective writing: Please comment on the applications of what you have learned from this module to dental research. (Minimum 1 sentence, maximum 100 words. You will be given 5 marks as long as you write something)

Price: $28.71

Solution: The downloadable solution consists of 14 pages, 1471 words and 20 charts.
Deliverable: Word Document