Question 1

You suspect that the salary of study participants might be skewed. A statistician told you that the skewed data should not be described by a mean. Why?

Accepted Answer

In a skewed data set, the mean is likely to be pulled towards the tail and does not provide a robust measure of the center. A median would be more appropriate.

Question 2

In preparing a grant, you meet with a biostatistician to discuss sample sizes. The biostatistician tells you that if you want more power, you will have to increase your sample size. Explain why this is the case. Provide additional alternatives for increasing the power of the study without changing the sample size.

Accepted Answer

As the sample size gets larger, the alternative sampling distribution gets skinnier. As a result, the null and alternative distributions become more separated. When there is a discernable difference between the two distributions, it is easier to reject the null hypothesis correctly, and thus increases the power of the study. Alternatively, as the a level increases, the statistical power also increases.

Question 3

Which of the following statements is considered a null hypothesis?

Accepted Answer

The null hypothesis is a statement of no effect, status quo, or no difference.

Question 4

Power, type 1 and type 2 errors are all related, which of the following statements is NOT true?

Accepted Answer

Type 1 and type 2 errors are inversely related. This means that as one increases, the other decreases.

Question 5

Suppose you are told that your BMI is 32, the 70th percentile for your age and sex. Interpret this percentile.

Accepted Answer

The answer of Suppose you are told that your BMI...

Question 6

A 2-year study was conducted to investigate bicycle safety at a city's 10 most congested intersections. The primary variable of interest was the number of accidents that involved a bicycle. Describe the number of accidents involving a bicycle as a continuous and ordinal variable.

Accepted Answer

The answer of A 2-year study was conducted to investigate...

Question 7

Central limit theorem states that the distribution of _________ will be normally distributed with large enough samples regardless of the shape of the population distribution.

Accepted Answer

The central limit theorem states that when large enough random samples are taken from a population, the distribution of those sample means will be approximately normally distributed, regardless of the shape of the population distribution, as long as the sample size is reasonably large (typically n ≥ 30).

Question 8

Which of the following is most likely a type 2 error?

Accepted Answer

The formal definition of a type 2 error is the probability of accepting a null hypothesis when it should be rejected. Since a null hypothesis typically states that there is no effect, type 2 error would be the probability of concluding that there is no effect when an effect truly exists.

Question 9

Briefly describe the difference between a bar graph and a histogram. Consider your own area of interest. Provide an example where a bar graph would be most appropriate. Provide an example where a histogram would be most appropriate.

Accepted Answer

The answer of Briefly describe the difference between a bar...

Question 10

A study was conducted to investigate whether the use of vitamins during prostate cancer treatment would improve the prostate-specific antigen (PSA). PSA in study patients was measured before treatment and four months after treatment. Suppose the change in PSA is 3.0 and there is a p-value of 0.07. How would you interpret this result?

Accepted Answer

The answer of A study was conducted to investigate whether...

Question 11

Which of the following is NOT an advantage of a retrospective study?

Accepted Answer

A retrospective study typically uses the data that are obtained before the initiation of the study. Thus, the investigators have no control over the way the variables are collected.

Question 12

How does the shape of the sampling distribution of means with sample sizes of N=10 and N=100 differ? How are they the same?

Accepted Answer

The answer of How does the shape of the sampling...

Question 13

John waited 30 minutes to be treated in an emergency room. A 30-minute wait is in the 20th percentile of the wait time. Did he have a comparatively long- or short wait time? Interpret this percentile.

Accepted Answer

The answer of John waited 30 minutes to be treated...

Question 14

Consider a study where the majority of the study subjects have high body mass index (BMI) and only a few have low BMI. When a histogram is constructed to describe the distribution of BMI, what shape of the distribution is most likely to be observed (right-skewed, left-skewed, or symmetric)?

Accepted Answer

The answer of Consider a study where the majority of...

Question 15

Twenty fibromyalgia patients are asked to register their pain on a visual analog scale (VAS), where 0 represents no pain and 5 represents the worst pain imaginable. The responses are {0, 0, 0, 1, 1, 2, 2, 3, 3, 3, 4, 4, 4, 4, 4, 5, 5, 5, 5, 5}.a.What are the frequency distribution and probability distribution of this sample? b.What are the mean, median, and mode for the VAS?

Accepted Answer

The answer of Twenty fibromyalgia patients are asked to register...

Question 16

In the following scenarios, state which type of error (type 1 or type 2) you would want to change in a hypothesis test to reduce errors.
A)You are investigating an effect of drug A indicated for patients who risk death if not treated. The drug will be used to replace a therapy that has serious side effects. The study is testing the hypotheses:
Null hypothesis: drug A is not effective.
Research hypothesis: drug A is effective. 
B)Many studies are investigating different experimental strategies for increasing bone density in osteoporotic women. Suppose a new therapy has been discovered to increase bone density in mice. It is possible that this therapy could be effective in humans.
The study is testing the hypotheses:
Null hypothesis: drug A is not effective.
Research hypothesis: drug A is effective.

Accepted Answer

The answer of In the following scenarios, state which type...

Question 17

A study was conducted to examine the gender difference in daily smoking prevalence.
A)State the null and research hypotheses for this test.
B)Suppose the p-value associated with the test is 0.04. What can you conclude?

Accepted Answer

The answer of A study was conducted to examine the...

Question 18

A group of investigators are interested in conducting a clinical trial to determine whether taking bio-identical treatments prevents postmenopausal osteoporosis in women. They obtained a list of physicians in the region and recruited their patients by mailing out response cards to all eligible women; 60% of the cards were returned and 75% of those respondents entered the study. They were equally divided into the treatment group and placebo group, and were followed for 5 years to determine if they develop osteoporosis. Identify the population, sample, sampling frame, and type of study.

Accepted Answer

The answer of A group of investigators are interested in...

Question 19

An outbreak of food poisoning occurred at a high school a few hours after 100 students ate lunch at the school's cafeteria. Most of them developed symptoms including nausea, vomiting, and diarrhea. An investigation was conducted to identify the contaminated food source. Interviews were conducted with students who ate at the cafeteria, and a food history was collected. Describe this study design (case-control, cohort, cross-sectional). Explain.

Accepted Answer

The answer of An outbreak of food poisoning occurred at...

Question 20

Suppose an investigator is comparing different infertility treatments. She hypothesizes that treatment A is better than treatment B. Describe what type 1 and type 2 errors would mean in this situation.

Accepted Answer

The answer of Suppose an investigator is comparing different infertility...

Quiz 1: An Overview of Statistical Concepts