please do all the three questions its urgent

please do all the three questions its urgent


• Option 2 – Observational Data handling and Analysis. Answer the following questions showing any working out where needed. All answers must be clearly labelled and inserted as task 3 into your workbook for submission. Task 3 Data analysis Option 2: Observational analysis (a) 200 children aged under 5 years were sampled from a village in Malawi using simple random sampling. All of the children were tested for malaria using a rapid diagnostic test. 51 of the children tested positive. Estimate the prevalence of malaria in children under 5 years old in the village and provide a 95% confidence interval for the estimate. • Make sure you read the questions thoroughly • Think about what the question is asking you to calculate first. • Think about what is required in a CI calculation • Summarize you findings for clarity Prevalence • Measure of frequency of existing cases = the proportion of people in a defined population that has the outcome at a specific point in time. • Prevalence = Number of existing cases at time (t) Study population at time (t) Calculating 95 % CI In 2 parts: 1. Work out the standard first (SE) SE – describes the precision of the sample mean (z value for 95% confidence = 1.96) Calculating 95 % CI 2. Calculate 95% CI (b) 40% of children had slept under a bed net the night before the survey. Of these 15% tested positive for malaria. • (i) Construct a carefully labeled two-way table for the data derived from the 200 children. • Think about the layout of the table exposure vs outcome • (ii) Estimate the odds ratio, risk ratio and risk difference for those who did not sleep under a bed net the night before compared to those that did. • Use your lecture notes for the equations • (iii) A statistician performed a χ2 test and obtained a p-value of 0.005. Interpret this result. Exposed Non-exposed Cases A Odds Ratio calculation using a 2 x 2 Table B Controls C D A + B C + D Total A + C B + D Odds Ratio Calculation • Ratio of the odds that the cases were exposed to the odds that the controls were exposed Odds Ratio Odds that a case was exposed OR Odds that a control was exposed Odds Ratio A / C OR B / D Odds Ratio A x D OR B x C Risk and odds • Observe a lecture theatre of 200 students for 1 hour • Outcome of interest is sneezing at least once 50 students sneeze during the lecture Risk of sneezing: 50/200 = 0.25 (or 25%) Odds of sneezing: 50/150 = 0.33 Rate or risk difference (RD) • the absolute (actual) difference between two rates or risks • subtract the rate in unexposed (r0) from the rate in the exposed group (r1) Rate (risk) difference = (r1 - r0) (c) • It has been suggested that families of higher socio-economic status are more likely to own bed nets and are also more likely seek malaria treatment when they are ill. Families have been grouped into three categories of socio economic status. • (i) Suggest a statistical technique that would let us examine the association between bed net use and malaria infection taking into account the differences in socio economic status. • (ii) Which of the three measures of association mentioned in part (b) will this technique produce? • (iii) Is the adjusted estimate likely to be closer to or further away from the null value than the unadjusted estimate from part (b)(ii)? Give a brief explanation for your answer. • Socio economic status considered a confounder here Final Comments on task 3 • Which ever option you chose read the questions carefully. • If you are asked to describe, comment, explain, interpret or give an example. Please do this! • Do NOT just calculate something and give the result without any explanation • Careful with rounding off • If you include tables and graphs discuss these • do not include results that you are not prepared to comment on • Label any graphs and tables for easy reference