Multiple Choice Questions MCQ

Question 65# Print Question

Parametric statistical methods make assumptions, which when satisfied make the fi nal estimate precise and accurate.

Which of the following is one such parametric assumption?

A. The distribution of observations in the population is not known

B. The variance of the compared samples are homogeneous

C. The analyzed variables are categorical measures

D. Outliers are unequally distributed

E. The sample size is at least 2% of the size of target population

Question 61# A 24-week RCT of memantine in moderate–severe Alzheimer’s dementia was reported. The investigators recruited 126 subjects for the memantine arm and 126 for the placebo arm, out of which 100 in the memantine group and 100 in the placebo group completed the study. Using a categorical measure of treatment response it was shown that 40% of the patients in the memantine group responded while only 20% in placebo group showed a response. Calculate the relative risk reduction of using memantine:
A. 20
B. 5
C. 2
D. 1
E. 10
D. Relative risk reduction (or relative benefit increase) is calculated using the following expression: relative risk reduction = absolute risk reduction/control event rate (RRR = ARR/ CER) The control event rate is 20%; the experimental event rate is 40%. Absolute risk reduction is the difference between the two event rates, i.e. 40 – 20 = 20% RRR = 20/20 = 1 Reference: Guyatt G and Rennie D, eds. Users’ Guides to the Medical Literature. A Manual for Evidence-based Clinical Practice.AMA Press, 2002, p. 660.

Question 62# A 24-week RCT of memantine in moderate–severe Alzheimer’s dementia was reported. The investigators recruited 126 subjects for the memantine arm and 126 for the placebo arm, out of which 100 in the memantine group and 100 in the placebo group completed the study. Using a categorical measure of treatment response it was shown that 40% of the patients in the memantine group responded while only 20% in placebo group showed a response. Using the above study results calculate the number needed to treat (NNT) for patients receiving memantine compared with placebo:
A. 20
B. 5
C. 2
D. 10
E. 7
B. The NNT can be calculated from the absolute risk reduction (ARR). NNT = 1/ARR NNT = 1/0.2 = 5 Five subjects must be treated with memantine to have one additional response. Reference: Guyatt G and Rennie D, eds. Users’ Guides to the Medical Literature. A Manual for Evidence-based Clinical Practice.AMA Press, 2002, p. 660.

Question 63# A 24-week RCT of memantine in moderate–severe Alzheimer’s dementia was reported. The investigators recruited 126 subjects for the memantine arm and 126 for the placebo arm, out of which 100 in the memantine group and 100 in the placebo group completed the study. Using a categorical measure of treatment response it was shown that 40% of the patients in the memantine group responded while only 20% in placebo group showed a response. If the above study used a per protocol analysis of primary outcome, the odds ratio of having a response is:
A. 2.7
B. 7.2
C. 0.16
D. 6
E. 0.37
A. To calculate the odds ratio, it will be useful to construct a 2 × 2 table. As per protocol analysis is used, only those who completed the trial have been included in the analysis. The odds ratio is obtained using the cross product ratio ad/bc = (80 × 40)/(60 × 20) = 8/3 = 2.7 Reference: Guyatt G and Rennie D, eds. Users’ Guides to the Medical Literature. A Manual for Evidence-based Clinical Practice. AMA Press, 2002, p. 660.

Question 64# Which one of the following measures is used in correlation analysis for non-parametric data?
A. Kappa statistics
B. Pearson’s correlation
C. Spearman’s correlation
D. Cohen’s d
E. Cronbach’s alpha
C. Spearman’s correlation is used for non-parametric correlation analysis. It is also called the rank correlation test. It can be used when one or both variables to be correlated consist of ranks (ordinal) or if they exist as quantitative data but do not have normal distribution. Pearson’s correlation is used for parametric correlation. Kappa is a measure of agreement not correlation. Cohen’s d is used to calculate effect size. The internal consistency of an instrument is tested using Cronbach’s alpha. Reference: Lawrie SM, McIntosh AM, and Rao S. Critical Appraisal for Psychiatry.Churchill Livingstone, 2000, pp. 72 and 75.

Question 65# Parametric statistical methods make assumptions, which when satisfied make the fi nal estimate precise and accurate. Which of the following is one such parametric assumption?
A. The distribution of observations in the population is not known
B. The variance of the compared samples are homogeneous
C. The analyzed variables are categorical measures
D. Outliers are unequally distributed
E. The sample size is at least 2% of the size of target population
B. To enable use of inferential statistics, standard sampling assumptions such as (1) the randomness of the sampled data and (2) the independent nature of the observations must be met. In addition, when parametric statistics are employed assumptions such as: Homogeneity of variance of the samples Observations are obtained from continuous (interval/ratio) scales Normal distribution of the observed variable must be met. There is no set proportion of population size that must constitute the sample size in order to use parametric statistics. But in samples that are too small the distribution may not be normal and the central limit theorem may not be applicable. In conditions where such assumptions are not met non-parametric statistics are used. The latter are often considered to be less robust. Reference: Bland, M. An Introduction to Medical Statistics, 3rd edn. Oxford University Press, 2000, p. 210.