An introduction to statistics I - Weebly



BJA CEACCP- STATISTICS MCQS

An introduction to statistics I

• 1. Regarding data:

a. A parameter is a measurable characteristic of a sample

b. A variable is a measurable characteristic of a population

c. A parameter has a fixed value

d. Interval data may be converted into categorical data

e. Ordinal data form a subset of categorical data

• 2. In a 2 × 2 contingency table:

a. The rows usually represent outcome

b. The upper row usually represents the control group

c. In order for it to be valid for statistical analysis, the observations must be independent

d. The cells may contain either frequency or relative frequency (%)

e. The cells must be either exhaustive or mutually exclusive

• 3. Regarding a histogram:

a. The x-axis is dimensionless

b. The rectangles may be of different width

c. The frequency within each class interval is always proportional to the height of the rectangle associated with that class interval

d. Class intervals of zero frequency must be included

e. Class intervals may be of unequal size

• 4. Considering two sets of paired interval data

a. When the data relate to two different methods of measuring the same variable, the correlation coefficient is not a good indicator of the comparative agreement between the two methods

b. The range of the Pearson correlation coefficient is between 0 and 1

c. A p-value < 0.001 for the correlation coefficient indicates a high correlation

d. The square of the Pearson correlation coefficient (r2) equals the amount of shared variance between them

e. The Pearson correlation coefficient is used for normally distributed data

Statistics II: Central tendency and spread of data

• 5. When determining the central tendency of a sample dataset:

a. The mode is always used for nominal categorical data.

b. The median is preferred to the mean for asymmetric distributions.

c. The mean is less susceptible to outliers than the median.

d. The mean is always preferred when the data are normally distributed.

e. The median of an even number of values equals the mean of the two central values.

• 6. Regarding measures of the spread of data about a central tendency:

a. The range is useful in statistical analysis.

b. There are three quartiles.

c. The interquartile range of a normal distribution equals ± 1 standard deviation.

d. The standard deviation of a sample equals √(∑i = 1i = n(xi − x̄)2/n).

e. A box and whisker plot may only be used to present normally distributed data.

• 7. A normal distribution:

a. Is fully described by its mean and standard deviation.

b. Is a probability curve with an area under curve (AUC) = 1.

c. May be positively skewed.

d. The mean and median are identical.

e. Has approximately 95% of the data lying within one standard deviation of the mean.

• 8. The standard normal distribution:

a. Has a mean of one.

b. Has z-values which indicate the number of standard deviations above or below the mean a given datum value lies.

c. Is a useful way of comparing data from two different normal distributions.

d. Has a kurtosis of one.

e. Has a skewness of zero.

Statistics III: Probability and statistical tests

• 9. The following statistical tests are appropriate for the data described:

a. Student's paired t-test – comparison of two groups of normally distributed data.

b. ANOVA - comparison of four groups of normally distributed data.

c. Student's unpaired t-test – comparison of two groups of data that are not normally distributed.

d. Mann–Witney U-test – comparison of three groups of data that are not normally distributed.

e. Fisher Exact test – analysis of a 2 × 3 contingency table.

• 10. Regarding Student's two sample t-tests:

a. There are two versions for use with normally distributed data and data that do not follow a normal distribution.

b. There is a series of t-distributions.

c. Should only be used if the sample standard deviations or variances are equal.

d. The unpaired version gives the same result as ANOVA for two groups of normally distributed data.

e. The paired version is more powerful.

• 11. A binomial distribution:

a. Approximates to a normal distribution as n increases.

b. May be used to describe a situation where there are n independent trials with two mutually exclusive outcomes.

c. Has a mean = n/p.

d. Has a standard deviation = np(1−p).

e. Can be used to predict the probability of obtaining 70 or more heads when a coin is tossed 100 times.

• 12. If two events A and B are considered:

a. P(A AND B) = 0 if they are mutually exclusive.

b. P(A OR B) = P(A) + P(B) if they are mutually exclusive.

c. P(A OR B) = 1 if A and B are exhaustive and mutually exclusive.

d. P(A AND B) = P(A) × P(B) if they are independent and not mutually exclusive.

e. P(A OR B) = P(A) + P(B) – P(A AND B) if they are independent and not mutually exclusive.

Statistics IV: Interpreting the results of statistical tests

• 13. Considering p-values:

a. If p < 0.05 and the null hypothesis is true, a type II error occurs.

b. If p > 0.05 and the null hypothesis is false, a type I error occurs.

c. The occurrence of type II errors may be reduced by performing a power calculation.

d. If p = 0.09 then the null hypothesis is rejected.

e. If p > 0.95, the 95% confidence interval for the difference between the means of two groups excludes zero.

• 14. The power of a statistical test:

a. Is greater when two groups of normally distributed data are compared than when two groups of data that do not follow a normal distribution are compared.

b. Is defined as (1 − α) × 100% where α is the probability of a type I error.

c. Increases with sample size.

d. Increases when a lower p-value for statistical significance is required.

e. When applied to a clinical study should be at least 50%.

• 15. Regarding statistical tests:

a. The null hypothesis proposes that there are no differences between study groups with respect to confounding variables.

b. A one-tailed test generates a smaller p-value than a two-tailed test for the same data.

c. Two tailed-tests are generally preferred.

d. A p value < 0.001 is highly clinically significant.

e. When comparing 10 study groups versus placebo, multiple t-tests are appropriate if the data is normally distributed.

Statistics V: Introduction to clinical trials and systematic reviews

•

• 16. Systematic reviews:

a. Are always quantitative.

b. Use Funnel plots to detect heterogeneity.

c. The ideal funnel plot is inverted and symmetrical.

d. Heterogeneity refers to differences in the trials that are combined.

e. Replication bias occurs if two similar studies give the same result.

• 17. Concerning clinical trial design:

a. Retrospective studies enable groups to be reliably matched and randomized.

b. The prevalence of a disease refers to the overall proportion of the population afflicted with a disease.

c. Misallocation bias is a feature of cross-sectional surveys.

d. Selecting every other patient in a clinic is a good method of randomization.

e. Prospective observational cohort studies may be randomized.

Clinical tests: sensitivity and specificity

• 18. A receiver operating characteristic (ROC) curve:

a. Is a plot of the false positive rate (x-axis) of a test and the true positive rate (y-axis).

b. Demonstrates how an increase in the false positive rate results in a decrease in the false negative rate.

c. Has an area under the curve (AUC) of 1.0 for a perfect clinical test.

d. Has an area under the curve (AUC) of zero if tossing a coin is used to determine whether or not a patient has a condition of interest.

e. Allows different clinical tests for the same condition to be compared.

• 19. The sensitivity of a clinical test:

a. Refers to the ability of a test to identify patients without the disease.

b. Equals true positives/(true positives + false positives).

c. Depends on the prevalence of the disease in the population.

d. Should be as high as possible when screening for a serious, preventable or treatable condition.

e. Defines how likely it is that a patient who tests positive has the condition.

• 20. The specificity of a clinical test:

a. Refers to the ability of a test to identify patients without the disease.

b. Equals true negatives/(true negatives + false positives).

c. Does not depend on the prevalence of the disease in the population.

d. Should be as high as possible when screening for a serious, preventable or treatable condition.

• 21. The positive predictive value of a clinical test:

a. Is influenced by the prevalence of the disease.

b. Will increase as the disease prevalence decreases.

c. Equals true positives/(true positives + false positives).

d. May be calculated using the Fisher's exact test.

e. Equals sensitivity/(1-specificity).

EBM

• 22. The GRADE system for grading the quality of the evidence involves:

a. (a) Identifying important or critical outcomes.

b. (b) Overall quality.

c. (c) Preliminary grading.

d. (d) Using a ‘gold standard’ group.

e. (e) Appreciating other factors.

• 23. Key elements which should be assessed when reviewing research evidence include:

a. (a) Directness.

b. (b) Bias.

c. (c) Consistency.

d. (d) Study quality.

e. (e) Study design.

• 24. Trade-offs are categorized as follows:

a. (a) Uncertain trade-offs.

b. (b) No net benefits.

c. (c) Uncertain benefits.

d. (d) Non-specific trade-offs.

e. (e) Net benefits.

• 25. The quality of evidence may be increased by:

a. (a) A dose–response gradient.

b. (b) Presence of plausible residual confounding.

c. (c) Imprecise data.

d. (d) Strength of association.

e. (e) Reporting bias

• 22. The GRADE system for grading the quality of the evidence involves:

(a) True; (b) True; (c) True; (d) False; (e) True

(a–e) The GRADE system for grading the quality of the evidence uses: identifying important and critical outcomes; preliminary grading in terms of study design, quality, consistency and directness; taking into account other factors; and the overall quality. Control groups are one of the fundamental principles which have evolved to minimize bias in a RCT, an example of which is the ‘gold standard’ group. Other types of control groups used in RCTs include placebo, ‘low dose’ group, ‘current standard’ group or historic control.

• 23. Key elements which should be assessed when reviewing research evidence include:

(a) True; (b) False; (c) True; (d) True; (e) True

(a–e) The quality of evidence indicates the extent to which one can be confident that an estimate of effect is correct. The four key elements of assessing quality of evidence are study design, study quality, consistency and directness. The quality of evidence provided by an individual study depends on the ability of the study design to minimize possible bias and to maximize attribution. A high risk of reporting bias is a factor which decreases the quality of evidence, but it is not one of the four key elements of assessing quality.

24. Trade-offs are categorized as follows:

(a) True; (b) True; (c) False; (d) False; (e) True

(a–e) A recommendation statement involves a trade-off between benefits and risks. As a concept trade-offs were introduced during the assessment of the risk-benefit of a specific intervention and they affect the strength of recommendations. They are categorized and defined as follows. Net benefits: the intervention clearly does more good than harm; Trade-offs: there are important trade-offs between the benefits and risks; Uncertain trade-offs: it is not clear whether the intervention does more good than harm; and No net benefits: the intervention clearly does more harm than good.

25. The quality of evidence may be increased by:

(a) True; (b) True; (c) False; (d) True; (e) False

(a–e) Factors increasing the quality of evidence include strength of association, evidence of a dose–response gradient and the presence of plausible residual confounding. Factors decreasing the quality of evidence include imprecise or sparse data and a high risk of reporting bias. [pic][pic][pic][pic][pic][pic][pic][pic][pic][pic][pic][pic][pic][pic][pic][pic][pic][pic][pic][pic][pic][pic][pic][pic][pic][pic][pic][pic][pic][pic][pic][pic][pic][pic][pic][pic][pic][pic][pic][pic][pic][pic][pic][pic][pic][pic][pic][pic][pic][pic][pic][pic][pic][pic][pic][pic][pic][pic]

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