B5.031 - Scholarly Projects

Question 1

when is mean preferred to measure central tendency for continuous data

Answer 1

symmetric distributions

Question 2

what is the mean sensitive to

Answer 2

extreme values and will be biased in presence of outliers

Question 3

when is median better for central tendency

Answer 3

for skewed distributions or distributions with outliers

Question 4

when is mode a preferred measure of central tendency

Answer 4

pretty much never

Question 5

what are SD and variance measures of

Answer 5

variability

Question 6

when is interquartile range the best estimate of variation of total

Answer 6

in the presence of outliers

Question 7

what will be higher mean or median

Answer 7

median, mean will be skewed low bc of the outlier

Question 8

what is a t test used for

Answer 8

to compare mean values between groups

Question 9

what are chi squared tests used for

Answer 9

test the difference between proportions between two groups

Question 10

when can correlation be evaluated

Answer 10

when comparing two continuous variables, (eg. height and weight are highly correlated)

Question 11

what is a risk ratio

Answer 11

a measure of effect calculated by dividing the risk of an outcome in one group by the risk of the outcome in a different group

Question 12

Researchers conducted a randomized controlled trial to test the efficacy and safety of oral BG-12 (dimethyl fumarate) at a dose of 240 mg two or three times daily as compared to placebo in patients with relapsing-remitting multiple sclerosis. Patients were randomly assigned to receive either oral BG-12 twice daily, oral BG-12 three times daily, or placebo (control). The investigators compared the average baseline Expanded Disability Status Scale (a score ranging from 0 to 10 with higher scores indicating a greater degree of disability) (EDSS) score of patients across the three treatment groups (twice daily, three times daily, placebo) and reported a p-value of 0.7. What statistical test did the authors conduct to produce this p-value?

Answer 12

ANOVA

Question 13

what is ANOVA

Answer 13

An ANOVA compares the mean of a continuous variable between two or more groups.

Question 14

the difference between ANOVA, Chi squared, t-test

Answer 14

An ANOVA compares the mean of a continuous variable between two or more groups. Though a t-test is also used to compare the mean of a continuous variable between groups, it is not appropriate for comparing more than two groups. A chi-square test compares proportions between groups.

Question 15

Researchers conducted a randomized controlled trial in 500 patients to test the efficacy and safety of catheter ablation for atrial fibrillation in heart failure patients. Patients were randomly assigned to undergo either catheter ablation or medical therapy (control). The primary outcome was the relapse rate over a period of 2 years. Two patients randomized to the catheter ablation group did not receive ablation. The authors implemented the intention-to-treat (ITT) principle and the outcomes for these 2 patients were included in the catheter ablation group. What is the best statement concerning the ITT analysis?

Answer 15

The results of the ITT analysis should not differ substantially from the per-protocol analysis because of minimal noncompliance. In this study, a small degree of non-compliance was observed and so the analytic sets for the ITT and per-protocol analysis will contain nearly the same set of subjects, resulting in relatively small differences in results from the two analysis methods.

Question 16

what is an ITT

Answer 16

An intent-to-treat (ITT) analysis is the most appropriate method for determining efficacy when analyzing a randomized controlled trial (RCT) because RCTs often suffer from noncompliance and missing outcome data. ITT analysis includes every subject who is randomized according to his or her randomized treatment assignment, ignoring non-compliance, protocol deviations, withdrawal, etc.

Question 17

what is the primary purpose of ITT

Answer 17

The primary purpose is to maintain the prognostic balance generated from the original random treatment allocation; however, in the presence of protocol deviations the ITT analysis generally provides a conservative (smaller) estimate of the treatment effect.

Question 18

what is a per protocol analysis

Answer 18

a per-protocol analysis limits the analysis to only those study subjects who were treated (and observed) according to protocol—this approach actually measures the beneficial effects of treatment in patients who completed treatment. When there is a large degree of non-compliance in a study, a per-protocol analysis will exclude a large percentage of study subjects’ data.

Question 19

Researchers aimed to evaluate the association between ASD and exposure to prenatal ultrasound. They conducted a case-control study that included 107 patients with ASD and 209 controls with typical development. Researchers created exposure categories of high and low. Given their study design, what measure of association would be the most appropriate for the authors calculate during data analysis to examine the relationship between ASD and ultrasound exposure level?

Answer 19

Odds ratio.

When a case-control study is conducted, risk cannot be directly calculated, since individuals are not followed forward in time to look for outcome incidence (new cases of disease). Instead, the odds of exposure among cases is compared to the odds of exposure among controls using an odds ratio.

Question 20

what is a hazard ratio

Answer 20

A hazard ratio is used when time to event data are available (from a forward-directional study like a cohort or randomized controlled trial; these study designs start with exposure and follow people forward to look for the development of an outcome of interest).

Question 21

when are risk ratio and rate ratios used

Answer 21

Both risk ratios and rate ratios are also used when incidence can be determined.

Question 22

when are prevalence ratios used

Answer 22

Prevalence ratios can be used in a variety of situations, but are used in special situations when a comparison of two prevalence values is needed (as the name suggests).

Question 23

Progesterone is essential for the maintenance of pregnancy. However, whether progesterone supplementation in the first trimester of pregnancy would increase the rate of live births among women with a history of unexplained recurrent miscarriages is uncertain. A recent systematic review reported on four small trials that examined the risk of miscarriage among women who received progesterone compared to the risk among women who received placebo or no treatment. An overall odds ratio of 0.39 (95% confidence interval [CI], 0.21 to 0.72) was reported, but the quality of the four trials was considered to be moderate to poor. What conclusions about the relationship between progesterone and the risk of subsequent miscarriage can be drawn from this study?

Answer 23

Early progesterone treatment reduced the risk of subsequent miscarriage.

Question 24

in meta analysis what type of ratio is usually calculated

Answer 24

In meta-analyses, an odds ratio is typically calculated. The four studies being used in the example are described as “trials”, suggesting randomized controlled trials. Thus, even though an odds ratio is calculated, inferences about risk can be made.