Assignment 1: module 1-3

MPH5041, 2013
Biostatistics for Clinical and Public Health Research
Test 3, Due April 26, 2013 by 11:59pm

Modules Covered: This Test covers Modules 1-5. All questions must be answered using
statistical knowledge in Modules 1-5 only. SPSS or any other statistical package can be used for
data analysis.
Assignment General Instructions:
This test is worth 5% of total marks for this subject. It will be marked out of 50
Please attach the relevant SPSS output (must be readable) either in the text or in an Please explain the results and make summary conclusion for each question in Word Limit: Maximum 950 Words (excluding tables).
Please download the “Test 3” and answer the questions within the WORD LIMIT
stated above and then upload the PDF file of the completed test by April 26,
11:59pm.
You must have a COVER PAGE, PRINT YOUR NAME, no sign required. See the
Section “Assignment and Test” on Moodle for cover page.
Instructions for Submission:
Please don’t add the data description or original tables/graphs given in the Questions to Upload the completed Test 3 onto Moodle under the “Test 3 Drop Box” section. Required Data: Cardiac Data and Prozac Data (see Assignment and Test Section on Moodle)
Extension: Students seeking an extension should contact Baki Billah before the due date. Please
note that an extension will not be granted without valid grounds (e.g., illness with medical
certificate).

Important Note:
If you submit more than one file as an attachment, only the first file will be assessed and rest of the files will be ignored, sorry!
Please use feedback/solution for Tests 1-2 as guidelines.
PLEASE DON’T discuss any of these questions on Discussion Forum.
Data Description: Consider a study that was conducted to investigate the risk factors for
mortality in cardiac surgery patients. Data was collected on Cardiac Surgery patients in public
hospitals in St Martine Island from 2005 to 2011. The risk factors for 30-day mortality (patients
died within 30-day of cardiac surgery) along with short name and their numerical codes (where
necessary) are shown in Table 1.

Table 1: Long and short name of selected variables for cardiac surgery patients
Risk Factor (Variable)
0 for elective 1 for urgent 2 for emergency 3 for salvage 0 for CABG only 1 for Valve only 2 for CABG + Valve 3 for others Any blank/dot “cell” in the data file indicates missing value
o 30-day mortality (MORT): patients who die within 30 days of cardiac surgery. o Ejection fraction: the % of blood the left ventricular pump off in each beat of heart. Questions 1 & 2 are related to “Cardiac Data” Question 3 is related to “Prozac Data”.
Note on SPPS output copy and paste: Please use “copy and paste special” option for all SPSS
output to copy, e.g., copy as “picture (Windows Metafile)” or “picture (Enhanced Metafile)” or
any other “picture” format available in your computer.
Question 1 [20 marks]: Using appropriate statistical method/s evaluate the significance of
difference in body mass index (BMI) of cardiac surgery patients between “yes” and “no”
diabetic. Note: Please attach SPSS (or any other package) output in the text or in an appendix.
Word Limit: Maximum 300 words.
Question 2 [10 marks]: Evaluate the significance of association between current smoking status
30-day mortality following cardiac surgery. Note: please use statistical method/s in Modules 1-5.
Show brief calculations. Word Limit: Maximum 200 words.
Question 3 [15 marks]: Suppose you wish to test the effect of Prozac on the well-being of
depressed individuals, using a standardised "well-being scale" that sums Likert-type items to
obtain a score that could range from 0 to 20. Higher scores indicate greater well-being (that is,
Prozac is having a positive effect). Pre test data was collected before the treatment and post test
data was collected after treated by Prozac. The mean of the pretest data is 3.33 and the mean of
the post test data is 7.0. The question is, "Is this a significant increase?" Assuming normality of
the data evaluate the question using appropriate statistical method/s. Note: Please attach SPSS
(or any other package) output in the text or in an appendix. Word Limit: Maximum 300 words.

Question 4 [5 marks]: Central Limit Theorem (page 63, Module 3): For a large sample size, the
distribution of the sample mean is normally distributed, even when the population distribution from which
the sample has been taken is decidedly non-normal (skewed).
Discuss why the distribution of sample mean follows the normal distribution even if the population
distribution is skewed. Word Limit: Maximum 150 words.

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