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Biostatistics Assignment -

In this assignment we take a published oral health research paper for statistical appraisal. As stated from the beginning of the course, statistical thinking needs to be embedded throughout a research project, from designing a study, collecting and analysing the data, to interpreting the results. The article is chosen not for its scientific value but for teaching/assignment purposes only.

Hence, the following questions are based on a paper relating to the effectiveness of using different types of toothbrush for plaque removal.

Erbe C, Klukowska M, Tsaknaki I, Timm H, Grender J, Wehrbein H. (2013). Efficacy of 3 toothbrush treatments on plaque removal in orthodontic patients assessed with digital plaque imaging: a randomized controlled trial,143(6):760-6. doi: 10.1016/j.ajodo.2013.03.008.

Questions -

1. Study Design

1.1 - Briefly describe the research question this paper aimed to answer.

1.2 - Apply PICO (population (P), intervention (I), comparison (C) and outcome(s) (O)) principle to identify each of the P-I-C-O elements of the study.

1.3 - State the type of study design used in this paper.

1.4 - From a research terminology view point, is this an experimental/observational, prospective/retrospective, cross-sectional/longitudinal study? Please justify your statement.

1.5 - Briefly describe a different study design (other than the one used in the paper) to compare the effectiveness of using 2 types of toothbrush in improving oral health. Comparing the study design you have just proposed to the one proposed by the authors, list two strengths and two weaknesses of the design you have suggested.

2. In most dental/medical research papers, a baseline characteristics table (such as Table 1 that appears in the article cited above) is displayed.

2.1 - For variables: "AGE", "SEX", "RACE", identify each variable's types (qualitative/quantitative, categorical/binary/ordinal/nominal/continuous/discrete).

Specify the summary statistics (Central tendency and Dispersion) the authors used for these variables.

2.2 - Propose (describe in words) a potential distribution for the variable "AGE" in the paper. Sketch your proposal using the following template. (Hint: Your answer should consider the current study design, together with the summary statistics reported on Table 1).

2.3 - Ignore the original study design for the current Question 2.3 and assume AGE is normally distributed. For a sample of 46 participants, it is reported that the mean and SD are 14.6 years old and 2.4 respectively.

2.3.1 Determine the age range that 70% of the participants (roughly 32 out of 46) fall into.

2.3.2 If another random sample of 46 participants was selected from the same population, what is the chance the average age of this new sample will be over 17 years old? Show your calculation and interpret the results.

2.4 - This study recruited subjects from the Department of orthodontics at the University Medical Center of the Johannes Gutenberg-University Mainz in Mainz, Germany. There are 86.9% White (race). Assume that in the city of Mainz the White population consisted of 70% total population who lives in the city. Conduct a hypothesis test to test if the proportion of the White population in the current study is equivalent to the same proportion of White race in Mainz city. Write down the null and alternative hypotheses, conduct the analysis, and briefly report your findings.

 2.5 - Provide 2 reasons why it is important to have such baseline characteristics tables in any medical/dental research?

3. Outcome/Analysis

3.1 - What is the outcome used in this study? What type of outcome is this variable (e.g. qualitative/nominal/ordinal/binary or quantitative/discrete/continuous)?

Provide the range of values this outcome variable can take.

3.2 - 3.2.1 State the procedure (e.g. the schedule of visiting the clinics, the treatment assignments) for how the outcomes were determined.

3.2.2 How many data points from each subject for each type of treatment (toothbrush), were collected over the whole treatment period?

3.2.3 For all the outcome data collected, are they independent or correlated to each other? Explain the reason for your answer.

3.2.4 For this question, take the study design into account. When the authors compared two treatment arms to each other (e.g. orthodontic electronic brush vs Manual brush), do the data collected for each treatment arm define two independent groups or two correlated groups? Explain your reason.

3.3 - Identify the main statistical model applied by the authors for analysing the efficacy of 3 toothbrushes on plaque removal. Although you may still feel unfamiliar with these statistical methods, the choice of statistical method was in order to accommodate the characteristics of the data. Suggest a characteristic of the dataset which may influence the choice of the statistical model you have just identified.

5. Sample Size

For this set of questions, use the information for sample size calculations that the authors had made under the "Statistical Analysis" section:

5.1 - List 4 key elements needed for the sample size calculation.

5.2 - Explain the terminology of "2-tailed alpha" and "power" using the sample size determination statement given by the authors.

5.3 - What is the sample size suggested by the sample size calculation? What is the total sample size that the authors have adopted in this study? Are these two numbers the same or different? Why?

5.4 - Will the sample size increase (or decrease), in comparison to the suggestion in the paper, if 2-sided alpha were changed to 20% from the original study design? Will the sample size increase (or decrease) if the power was changed to 95%?

Attachment:- Assignment Files.rar