Country : Australia
Assignment Task :

Introduction 

This assignment assesses your understanding of topics discussed in Modules 1 to 6 of the course but focuses mainly on Modules 4 to 6. 

It is important to present your answers to all questions with appropriate precision (i.e. in tables, figures and text). Tables and figures should be presented in the way you would present them in a scientific journal or a standard report. You should follow the presentation guidelines you have been given in the course. When asked to write a conclusion or interpret values, your answer should include relevant values you have calculated, and other data provided to you. 

You will need to use Stata to answer Question 1 and Question 2. Question 3 requires you to read the edited extract on Page 7. 

 

Question 1

A randomised controlled trial was conducted to assess the effectiveness of a new eye drop to reduce eye pain in patients suffering from a systemic condition affecting both eyes. Each patient received the prescribed dose of the new eye drop in one eye and the same dose of an existing drop in the other eye. The investigators randomised which eye was treated with the new eye drop and which received the existing eye drop. 45 patients were asked to rate the level of pain in each eye on a 0–10 scale with higher scores indicating higher levels of pain. 

The dataset is provided on Moodle in the Excel file AssignQ1.xls. The dataset contains the following variables. 

• ID: Participant ID number 

• Pain_ctl = pain score in the eye receiving the existing drop 

• Pain_new = pain score in the eye receiving the new drop 

 

a) What are the study factor and the outcome factor?

b) State the null hypothesis and alternative hypothesis for the study.

c) Which statistical test would be appropriate to test the null hypothesis you have stated and why? 

d) Use Stata to conduct the statistical test you stated in part (c) report the key findings and interpret them. Before using the test, check the data to see if the assumptions required for the test are met. Report all the relevant statistics and graphs required for checking the assumptions with interpretations.

e) Write a brief report summarising all the results you have obtained and state your conclusion. 

 

Question 2 

A prospective cohort study was conducted over a period of 10 years to investigate whether there is an association between smoking and stroke. The study population was 15,000 people selected at random from a national government funded health insurance database. 

PART A Table 1 shows the results of a pilot study comparing self-reported current smoking status and the current smoking status determined using a gold standard method.

Comparison

 

a) From the results of the study shown in Table 1, 

i. Calculate the sensitivity and specificity of using self-reported smoking status compared to the gold standard test. Show your working. 

ii. Calculate the 95% confidence intervals using Stata, reporting the relevant output.

iii. Report and interpret the meaning of each of the measures you have calculated. 

b) Would using self-reported smoking status impact on the validity of a study investigating the effect of smoking on stroke? Provide reasons to support your answer. 

 

PART B 

A clinical examination was conducted on all participants at baseline. The researchers collected information on demographic information, such as age and sex, health behaviours such as past and current smoking status and exercise, medications and participants’ medical history. The researchers had access to data on every visit to a doctor or hospital for each study participant, as well as the death records of study participants which they used to determine whether study participants had a stroke or died from a stroke. 

Of the 15,000 participants randomly selected for the study, 1,000 already had a history of stroke and were excluded. Of the remaining study participants, full data were available for 11,000 participants. The study investigators found that 2,200 of the remaining 11,000 study participants reported being current smokers at baseline. A total of 500 of the 11,000 study participants had a stroke during the study period, of whom 167 were current smokers at baseline. 

a) Why did the investigators exclude the 1,000 people who had previously had a stroke at the beginning of the study?

b) Were there any important problems with selection bias in this study? Provide reasons to support your answer. 

c) Draw a 2 x 2 table to display the study data of the association between current smoking and stroke.

d) Calculate the relevant measure of association and its 95% confidence interval using Stata. Show the relevant Stata output and write a conclusion.

e) The investigators wanted to investigate if the proportion of smokers in the study sample of 11,000 participants was a true representative of the target population with respect to the prevalence of smoking. According to the most recent national census the prevalence of smoking in the target population is 11%. 

i. State the null and alterative hypothesis for this. 

ii. Conduct an appropriate statistical test to evaluate the hypothesis you mentioned in part i. Mention the name of the statistical test you have chosen, explain the reason for choosing the test and report the relevant Stata output with an interpretation of the findings.

f) The investigators analysed the data further to assess whether there was an association between smoking and death due to stroke. They also wanted to know whether age gender was a confounder or effect modifier of the association between heavy smoking and death due to stroke. They calculated the following values: 

i. All participants - heavy smoking and death due to stroke: RR = 2.5

ii. Male Participants - heavy smoking and death due to stroke: RR = 2.2 

iii. Female participants - heavy Smoking and death due to stroke: RR = 3.5 Is gender a confounder or effect modifier of the association between smoking and death due to stroke? Give reasons for your answer

 

Question 3 

Read the edited extract from a published study shown below. Use the information contained in the extract to answer the following questions. 

(a) Using PICO format, write the research question for the study. 

(b) What study design was used? Is this the best study design to answer this question? Give reasons for your answers. 

(c) (i) Describe the source population and the study participants.

(ii) Describe any strengths and potential biases in the selection of participants into this study, giving reasons for your answers. 

(d) (i) What were the study factor and the outcome factor? (ii) Describe one strength and one limitation in the measurement of the study factor. Give reasons for your answers. 

(e) How have the authors dealt with potential confounders in this study? Is there potential for confounding to affect study results? Give reasons for your answers.

(f) What is your assessment of the internal and external validity of the study findings? 

 

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