1. Question-Bank @UWE_KAR
Practice & Communication of Science
Question-Bank
@UWE_KAR

2. Notes for exam Pen, pencil, eraser and ruler
Your own Cambridge Stats book
No writing (but highlights, tabs OK)
We will check
UWE-approved calculator
We provide a ‘formula sheet’ at back of exam
Can’t guarantee 100% that 4 questions covering 4 topics won’t all be the same topic
Sec A (30%), Sec B (30%), Sec C (40%)
3h exam, so about min per %

3. Variation Q7
Explain the meaning of the terms repeatability and reproducibility, clearly defining the difference between the two.
repeatability – short-term, limited variation (eg same lab, operator, equipment)
reproducibility – long-term, extended variation (eg different lab, operator, equipment, day)
Two methods were used to determine the volume of a subject’s hand. Both were tested by taking three measurements on one Monday and three on the following Friday. The following results were obtained.

4. Variation Q7
Which method used on the Monday was more variable, and why?
  CoV = SD/mean*100
Monday method A vs Monday method B?

5. Variation Q7
Suppose a larger study (with 200 observations) found the mean volume for hand size to be 261.2cm3 and the standard deviation of hand size (volume) to be 10.3cm3, calculate at 95% confidence interval for mean hand size (volume).
95% CI = mean +/- t(0.025, n-1) x sd/sqrt(n)
/ x 10.3/sqrt(200)
/ x 0.728 / ,

6. Chi Q7
A final year student investigating the so-called ‘ACE’ gene took a sample of 140 male students and genotyped them. She found the following:
aa Aa AA
Number of students
In principle the ratio should be 1 : 2 : 1
a) Test whether the data are compatible with the theoretical ratio.

7. Chi Q7 aa Aa AA Number of students 26 75 39
aa Aa AA
Number of students
total = 140, split 1+2+1=4 ways = 35
expected = 35 : 70 : 35
chi-sq = ((26-35)^2/35) + ((75-70)^2/70) + ((39-35)^2/35)
= = 3.13
critical value (5%, 2 df) is 5.991
3.13 < so cannot reject H0

8. Chi Q7 b) Give a 95% CI for the % of AA in student pop. aa Aa AA
Number of students
% AA = 39/140*100 = 27.86%
95% CI for a proportion is…
so it’s / * sqrt(27.86( )/140)
(using Table 5 to get 1.96; ie a 2-tail 2.5%)
= / * 3.789
= /- 7.43
or (20.43, 35.29)

9. Non-parametric Q6
 In a study to investigate whether people of similar heights tend to date each other, 10 couples were selected and their height in inches recorded.  
Calculate Spearman’s Rank Correlation Coefficient, and test whether there is a significant correlation between heights of the women and men in the couples.

10. Non-parametric Q6 Calculation… separately rank the X and the Y values
calculate the diffs between each XY pair of ranks
square them, then sum them (sumdsq)

11. Non-parametric Q6 Calculation… Rank Coeff = 1 – ( 6sumdsq / n(n2-1) )
= 1 – ( 6x80.5/ 10(10x10-1))
= 1 – 483 / 10x99
= 1 – = 0.512
Critical R (2.5%, n=10)
Our Rank Coeff needs to be > critical to reject Null Hypo
H0: No correlation between male/female heights in couples
H1: Correlation between male/female heights in couples

12. Proportions Q6
 The Journal of the American Medical Association (April 18, 2001) published a study on the effectiveness of using extracts of the herbal medicine, St. John’s wort, in treating major depression. In an 8-week randomised, controlled trial, 200 patients diagnosed with major depression were divided into two groups; one group of 98 patients receive St. John’s wort extract, while the remaining patients received a placebo. At the end of the study period, 14 of the St. John’s wort’s patients were in remission compared to 5 of the placebo patients. Is St. John’s wort effective in treating major depression? (The greater the number in remission, the more effective is the treatment). Conduct a suitable significance test at the 5% sig. level.

13. Proportions Q6 P1 = 14/98x100 = 14.29% P2 = 5/102x100 = 4.9%
Pbar = 19/200x100 = 9.5%

14. Proportions Q6
z = – 4.9 /
sqrt(9.5( )/ ( )/102)
= 9.39 / sqrt( )
= 9.39 / = 2.276
critical t 5% (n>120) = 1.645
better to use 2.5% as StJW could have –ve effect?
some evidence that StJW has an positive effect