Статистическая викторина Британского медицинского журнала
 

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Study design

A neurologist wanted to study the risk of stroke and transient ischaemic attack in people with a diagnosis of migraine. From her headache clinic she selected cases of migraine and controls without migraine. She collected stroke and transient ischaemic attack outcomes by writing to all subjects and their general practitioners five years later. Which study design best describes what was done?


a Ecological study

b Cohort study

c Clinical trial

d Case-control study

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Conditional probabilities

Mike has only two children, and they are called Pat and Alex, which could equally be boys’ or girls’ names. In fact, Pat is a girl. What is the probability that Alex is a boy?

a 50%

b Slightly less than 50%

c Slightly more than 50%

d Between 60% and 70%

e Between 40% and 30%

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Measures of spread

Which, if any, of the following are measures of spread?


a) Mode

b) Interquartile range

c) Skewness

d) Variance

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Multiple linear regression


Which, if any, of the following statements are true of multiple linear regression?


a It may be used to control confounding in cohort studies

b It can only assess a linear (straight line) relationship between variables

c It gives misleading results when two or more independent variables are highly correlated

d It can be used with dichotomous or categorical independent variables

e It can be used with dichotomous or categorical dependent variables

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Probability and prevalence


If the prevalence of blood group O negative is 9%, what is the probability that among four randomly chosen unrelated people none will be O negative?


a) 36%

b) 64%

c) 66%

d) 69%

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Outcome measures in case-control studies

Используя записи врачей общей практики было выполнено исследование типа "случай-контроль" для того, чтобы выяснить, является ли диета с низким содержанием растительных волокон фактором риска развития синдрома раздраженного кишечника. Сто свежих случаев СРК и 200 случайным образом отобранных других пациентов были взяты из отчетов врачей общей практики для проведения опроса. Что из нижеперечисленного еще могло бы быть оценено путем этого же исследования?

a) The prevalence of smoking in the practice population

b) The hazard ratio of a low fibre diet for irritable bowel syndrome

c) The odds ratio of a low fibre diet for irritable bowel syndrome

d) The prevalence of irritable bowel disease in the practice population

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Non-parametric tests


Which if any of the following statements are false?


a) Non-parametric statistics may be used for normally distributed data

b) Correlation coefficients are inappropriate for non-normally distributed data

c) Medians are always a more valid way than means are to compare non-normally distributed data

d) The significance level of a test should be increased when multiple tests are made in a study

Там по ссылкам можно проверить себя и прочитать правильный ответ с разъяснениями :)

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Matching the test to the problem


Which of the following statistical tests would be your first choice in each of the studies below?


Test:

1 x2 for contingency tables

2 Two sample t test

3 Log rank test

4 Poisson test

5 Pearson’s correlation coefficient

6 Paired t test

Study:

a) The occurrence of heart attacks on duty in the staff of two airlines

b) Change in uric acid concentrations in people with gout before and after starting a new diet

c) Cholesterol concentrations in people from high and low income households in a health survey

d) The association of car colour with owner’s personality type

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Interpreting a low P value


When a health authority introduced a new community based vaccine promotion team, vaccination rates for the MMR (measles, mumps, rubella) vaccine improved over the next two years. The improvement was statistically significant, with a one sided P value of less than 0.01. Which of the following, if any, are true?


a) Confounding is unlikely because of the low P value

b) If the vaccination rates were varying randomly over time then the probability of a result like this or better would be less than 1 in 100

c) The difference in vaccination rates is likely to be important

d) The team approach can be recommended as better than the old approach

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Comparing length of stay


The mean length of stay in one hospital after stroke was 21 days, the median was 12 days, and the standard deviation was 13 days. Which of the following, if any, are true?


a) The typical length of stay was 21 days

b) The mean length of stay may be affected by long stay patients

c) As many patients stayed for fewer than 12 days as stayed longer than 12 days

d) When comparing length of stay in this hospital with that in another hospital, survival methods would be preferable to a t test

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Uncontrolled studies


To measure the effect of a food supplement on headaches, a questionnaire survey was sent to a random sample of workers in one factory. People who scored in the top 20% for frequency of headaches in the previous two weeks were invited to "try a natural food supplement used to treat headaches." A follow-up questionnaire two weeks later showed markedly fewer headaches. Which, if any, of the following could affect the results?


a) The Hawthorne effect

b) Regression to the mean

c) Healthy worker effect

d) Placebo effect

e) Confounding by indication

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Crossover trials


Which of the following statements apply to crossover clinical trials?


a) They are not subject to confounding by age, sex, or most personal characteristics

b) Randomisation is not possible

c) They are useful in studies using mortality as the endpoint

d) They need fewer people than parallel group trials

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Incidence and prevalence

The average survival after a diagnosis of multiple sclerosis is much longer than after a diagnosis of cervical cancer. They both have about the same incidence of five per 100 000 per year, although this varies with geography and demography. In a large population the prevalence of multiple sclerosis would then be expected to be:


a) The same as that of cervical cancer

b) Much less than that of cervical cancer

c) Much greater than that of cervical cancer

d) Less than the incidence of multiple sclerosis

e) Greater than the incidence of multiple sclerosis

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Correlation

A study finds a correlation between two variables (r=0.06), but this outcome is not statistically significant. Which, if any, of the following could be correctly used to describe the data?


a) High values of one variable are associated with low values of the other

b) For every unit change in one variable the other variable increases by 0.07

c) There is a strong linear association but the sample size is too small to demonstrate it

d) The significance should be quoted as 0.06 rather than "not significant"

e) There does not appear to be a linear association between the variables