08 Oct Surgeons at Hospital A report that the mortality rate at the end of a one-year follow-up after a new coronary bypass procedure is 15%.

Epidemiology and Biostatistics for Public Health Application 2

Question 1Surgeons at Hospital A report that the mortality rate at the end of a one-year follow-up after a new coronary bypass procedure is 15%. At Hospital B, the surgeons report a one-year mortality rate of 8% for the same procedure. Before concluding that the surgeons at Hospital B have vastly superior skill, which of the following possible confounders would you examine?

 

   The severity (stage. of disease of the patients at the two hospitals at baseline

 

The starting point of the one-year follow-up at both hospitals (after operation versus after discharge.

 

Difference in the postoperative care at the two hospitals

 

Equally thorough follow-up for mortality

 

All are correct.

 

Question 2In a study to determine the incidence of a chronic disease, 150 people were examined at the end of a three-year period. Twelve cases were found, giving a cumulative risk of 8%. Fifty other members of the initial cohort could not be examined; 20 of these 50 could not be examined because they died. Which source of bias may have affected the study?

 

Information bias: interviewer/abstractor bias

 

Hawthorne effect

 

Selection bias: survival bias

 

Information bias: recall bias

 

Question 3An epidemiologic experiment is performed in which one group is exposed to a suspected factor and the other is not. All individuals with an odd hospital admission number are assigned to the second group. The main purpose of this procedure is to:

 

ensure a double-blind study.

 

prevent observer bias with respect to the factor.

 

prevent observer bias with respect to the outcome.

 

improve the likelihood that the two groups will be comparable with regard to known and unknown confounding factors.

 

guarantee comparability of the two groups with regard to other relevant factors.

 

Question 4Which of the following is an independent-measures design?

 

All participants perform in all conditions.

 

Each participant is tested twice, once in each condition.

 

Different participants perform in each condition.

 

None of these are correct.

 

 

 

Question 5What does the error bar on an error bar chart represent?

 

The confidence interval round the mean.

 

The standard error of the mean.

 

The standard deviation of the mean.

 

It can represent any of a, b or c.

 

Question 6A double-blind study of a vaccine is one in which:

 

the study group receives the vaccine and the control group receives a placebo.

 

neither observers nor subjects know the nature of the placebo.

 

neither observers nor subjects know which subject receives the vaccine and which receives a placebo.

 

neither the study group nor the control group knows the identity of the observers.

 

the control group does not know the identity of the study group.

 

Question 7An independent t-test is used to test for

 

Differences between means of groups containing different people when the data are normally distributed, have equal variances and data are at least interval.

 

Differences between means of groups containing different people when the data are not normally distributed or have unequal variances.

 

Differences between means of groups containing the same people when the data are normally distributed, have equal variances and are at least interval.

 

Differences between means of groups containing different people when the data are not normally distributed or have unequal variances.

 

Question 8From the table below, did the independent variable have an effect?

 

Yes, there is a statistically significant effect.

 

Yes, but the effect was not statistically significant.

 

Not enough information.

 

No, it is not statistically insignificant.

 

Question 9The purpose of a double-blind study is to:

 

achieve comparability of cases and controls.

 

reduce the effects of sampling variation.

 

avoid observer and interviewee bias.

 

avoid observer bias and sampling variation.

 

avoid interviewee bias and sampling variation.

 

 

 

Question 10Which of the following would you consider to be an example of repeated-measures design?

 

6 participants are given analgesia and 6 a placebo; effects of pain relief after 4 hours is recorded.

 

12 participants are given analgesia, 6 are asked to record pain level after 2 hours and the remaining 6 participants after 4 hours.

 

12 participants are asked to record pain level after 4 hours then given analgesia.

 

None of the these are examples of repeated-measures design

 

Question 11You are investigating the role of physical activity in heart disease and suggest that physical activity protects against having a heart attack. While presenting these data to your colleagues, someone asks if you have thought about confounders such as factor X. This factor X could have confounded your interpretation of the data if it:

 

is a factor for some other disease, but not heart disease.

 

is a factor associated with physical activity and heart disease.

 

is a part of the pathway by which physical activity affects heart disease.

 

has caused a lack of follow-up of test subjects.

 

 Question 12Participants take a simulated driving test twice. In one condition they have no alcohol, in the other they have enough alcohol to take them over the legal limit. What type of design is this?

 

Repeated-measures

 

Related-measures

 

Between-subjects

 

Independent-measures

 

Question 13What is important to understand about differences between variables?

 

Relationships can be established.

 

Random studies can be undertaken.

 

Causal inferences can be made.

 

Relationships between variables can be significant.

 

Question 14From the table below, indicate how many people took part in this experiment?

 

37

 

38

 

39

 

40

 

Question 15The strategy that is not aimed at reducing selection bias is:

 

   development of an explicit case definition.

 

encouragement of high participation rates.

 

standardized protocol for structured interviews.

 

enrollment of all cases in a defined time and region.

 

Question 16Which of the following is a technique to reduce information bias?

 

Use memory aids and validate exposures.

 

Provide standardized training sessions and protocols.

 

Use standardized collection forms.

 

Try to ensure that questions are clearly understood.

 

All are correct.

 

Question 17A repeated-measures design would be appropriate for which of the following situations?

 

A researcher would like to study the effect of alcohol on reaction time.

 

A researcher would like to compare individuals from at least two populations.

 

The effect of a new treatment is studied in a small group of individuals with a rare condition.

 

a and b.

 

Question 18When using the independent t-test which assumption(s) should be made?

 

Normally distributed sample

 

Homogeneity of variance

 

Data at least categorical

 

a and b

 

Question 19What was the dependent variable in the table below?

 

Variances

 

Number correct

 

Equal assumptions

 

Not given in table

 

Independent Samples Testt-test for Equality of Means

 

tdfSig. (2-tailed)

 

number correctEqual variances assumed10.99138.000

 

Equal variances not assumed10.99130.727.000

 

Question 20In a t-test to determine whether analgesia or a placebo provide pain relief, the t-value obtained for the two-tailed probability p is found to be a low number at p = .042. What can be deduced about this result? of your textbook for more information on this question.

 

There is a 4.2% chance that the null hypothesis will be true.

 

There is a 2.1% chance that the null hypothesis will be true.

 

There is a 4.2% chance that the null hypothesis will be false.

 

There is a 2.1% chance that the null hypothesis will be false.

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