Wolkite University
College of Natural and Computational Sciences
Department of Statistics
Advanced Biostatistics Assignment for Biology Department Post Graduate students [30%]
Instruction:
 The Analysis should be done using SPSS
 Hypothesis, level of significance, decision and interpretation should be put
in your answer.
 Any form of plagiarism resulted ZERO grade for both
 Due date: February 30, 20213 E.C
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1. A massive multistate outbreak of food-borne illness was attributed to Salmonella
enteritidis. Epidemiologists determined that the source of the illness was ice cream. They
sampled nine production runs from the company that had produced the ice cream to
determine the level of Salmonella enteritidis in the ice cream. These levels (MPN/g) are
as follows:
0.593; 0.142; 0.329; 0.691;
0.231;
0.793; 0.519; 0.392; 0.418
Use these data to determine whether the average level of Salmonella enteritidis in the ice
cream is 0.3 MPN/g. (Use = 0.01)
2. The concentration of mercury in a lake has been monitored for a number of years.
Measurements taken on a weekly basis yielded an average of 1.20 mg/m (milligrams per
cubic meter) with a standard deviation of 0.32 mg/m. Following an accident at a smelter
on the shore of the lake, 15 measurements produced the following mercury
concentrations.
1.60 1.77 1.61 1.08 1.07
1.79
1.34
1.07 1.45 1.59 1.43 2.07 1.16 0.85 2.11
a. Give a point estimate of the mean mercury concentration after the accident.
b. Construct a 95% confidence interval on the mean mercury concentration after the
accident. Interpret this interval.
c. Is there sufficient evidence that the mean mercury concentration has increased
since the accident? (Use = 0.05)
3. Company officials were concerned about the length of time a particular drug product
retained its potency. A random sample of n1 10 bottles of the product was drawn from the
production line and analyzed for potency. A second sample of n2 10 bottles was obtained
and stored in a regulated environment for a period of 1 year. The readings obtained from
each sample are given below.
Fresh
10.2 10.5 10.3 10.8
Stored 9.8
9.6
10.1 10.2
9.8
10.6
10.1 9.7
10.7 10.2 10.0
10.1
9.5
9.9
9.6
9.8
a. Estimate means, Variance and Standard deviation for both fresh and stored
drug.
b. Estimate the 95%confidence interval for the mean difference and
comment on the result?
4. The tensile strength of Portland cement is being studied. Four different mixing techniques
can be used economically. The following data have been collected:
Tensile strength (Ib/in2)
Mixing
technique
1
3129
3000
2865
2890
2
3200
3300
2975
3150
3
2800
2900
2985
3050
4
2600
2700
2600
2765
a. Test the hypothesis that mixing techniques affect the strength of the cement (Use
= 0.05)
b. Use LSD method with = 0.05 make comparison between pairs if means?