B4.027 - Study Design

Question 1

what is systematic review used for

Answer 1

The aim of a systematic review is to conduct a comprehensive survey of the literature, both published and unpublished, to address a specific clinical question. A systematic review follows a detailed plan to search the literature, using reproducible methods. When conducting a systematic review, it is critical to organize information and provide accurate attribution to sources (using a citation management software program is an easy way to do this). An UpToDate article is a type of systematic review, but not a study design itself.

Question 2

Infants <6 months old with influenza are at risk for adverse outcomes. Researchers are designing a cohort study to investigate the impact of the influenza vaccine on infants born to mothers who received the vaccine during pregnancy. The primary outcome is defined as influenza hospitalization of the infant in the 6 months after birth. What key piece of information do the researchers need to specify next?

Answer 2

While all of the other components listed are important to study design and protocol development, the next factor to be clearly identified is the population to be included in the study. How will participants be identified? From where?

Question 3

Researchers are interested in understanding the impact of eating a diet high in vegetables on health. They design a long-term cohort study and enroll a group of college freshmen. At baseline, researchers ask participants about their dietary intake. Annual dietary assessments will occur throughout the study. These participants will be followed for 30 years to evaluate the relationship between diet and health outcomes. Which of the following options represents an optimal end-point clinical outcome that the researchers could use as a primary outcome for their study?

Answer 3

Death due to any cause is a clinically important outcome. A clinical outcome directly measure how a patient feels, functions, or survives. The other options are surrogate endpoints. These conditions might lead to a clinically important outcome, but are only substitutes. Whenever possible, the primary endpoint of a study should be clinically important (an end-point clinical outcome. However, surrogate outcomes (like blood pressure and BMI) are sometimes faster, easier, and cheaper.

Question 4

The first published study examining the association between Reye’s syndrome and aspirin use among children was performed in Arizona in December 1978. Seven school-aged children with Reye’s syndrome were compared to 16 classmates, matched for sex and suffering from an illness during the same month as the cases. What is the primary reason that the authors used a case-control design to address this study question?

Answer 4

A case-control study design is an excellent study design to use when the outcome of interest (Reye’s syndrome) is rare. Because the study population is classified on the basis of disease status (Reye’s syndrome-cases; no Reye’s syndrome-controls), cases can be actively sought.

Question 5

To evaluate the relationship between type of birth (vaginal birth or Cesarean-section) and adverse birth outcomes, researchers analyze population-level data from the Canadian province of Quebec. Women who gave birth vaginally are defined as the unexposed group, and women who had a C-section performed are defined as the exposed group. Study staff review hospital records to capture information on adverse birth outcomes in the week following delivery (infant mortality, low birthweight, maternal complications). What study design is being used here?

Answer 5

Cohort study

Question 6

what is a cohort study

Answer 6

A cohort study is a type of observational study. In this example, researchers are analyzing existing data and categorizing women on the basis of exposure (vaginal birth vs. C-section); then, women are followed forward in time to look for the outcome of interest (adverse birth outcomes). The study “follows” women and their infant for one week after the exposure occurred.

Question 7

what is a case control study?

Answer 7

In a case-control study, another observational study design, participants are classified on the basis of disease status; then, researchers look backwards in time to look for a history of exposure.

Question 8

what is a cross sectional study?

Answer 8

Cross-sectional studies assess the exposure and outcome at one point in time.

Question 9

what are ecologic studies?

Answer 9

Ecologic studies compare populations.

Question 10

When conducting a randomized controlled trial to evaluate the impact of a new treatment compared to a standard treatment on the incidence of disease, what is the primary purpose of randomization?

Answer 10

Randomization allows for an unbiased assignment of study participants to one exposure group or another. Because the only factor being assigned is the exposure, randomization ensures that the exposure groups are balanced on all other factors. Randomization allows for a straight-forward analysis of an exposure-disease relationship (an intention-to-treat analysis).

Question 11

A large pharmaceutical company has developed a new laboratory test for the detection of N. gonorrhoeae. They are interested in licensing the test for commercial use though the Food and Drug Administration (FDA). To determine the new test’s performance characteristics and capture data for their application, what study design could be used?

Answer 11

Cross-sectional study

Question 12

what is the best study for comparing two tests and how does it work

Answer 12

The most common study design to determine medical test performance is a cross-sectional study. Specimens are taken from a single individual; then, these specimens are run concurrently using different test platforms. One of these tests is identified as the “gold standard”. The results from the test under evaluation are compared to the gold standard results, and test performance characteristic are calculated.

Question 13

what is meta analysis

Answer 13

A meta-analysis involves the compilation of data from multiple studies to answer a study question that has been addressed repeatedly in the literature.

Question 14

describe a cohort study

Answer 14

A cohort study is a study design with forward directionality, following participants to capture the incidence of an outcome of interest.

Question 15

describe a cross over study

Answer 15

A case-crossover study design allows for one individual to serve as their own control (each individual receives both the intervention and control in sequential order).

Question 16

Prostate-specific antigen (PSA) level in midlife predicted future prostate cancer mortality in an unscreened Swedish population. Researchers were interested in conducting a study to determine if a baseline PSA level during midlife predicted lethal prostate cancer in a US population with opportunistic screening. What is the strongest study design that these researchers might use to answer their study question?

Answer 16

A cohort study is a study with forward directionality. Participants are enrolled and followed forward in time to see if they develop the outcome of interest. In this case, researchers could enroll a group of men in mid-life, measure their PSA, then follow them for some time (5-10 years might be reasonable). A cohort study provide strong evidence of temporality; the exposure of interest is observed before the outcome of interest is observed.

Question 17

describe a case control study

Answer 17

A case-control study is a backwards directional study where participants are defined on their disease status. Then, researchers look backwards in time to assess the exposure.

Question 18

describe a case series study

Answer 18

Case-series studies are just descriptive studies of unusual presentations.

Question 19

The physical examination records of the incoming first-year class of 1935 at the University of Minnesota were examined in 1980 to see whether the freshmen’s recorded height and weight at the time of admission to the university were related to their chance of developing coronary heart disease by 1980. What study design would be the best to address this scenario?

Answer 19

The study design presented here is for a retrospective cohort. The study started in the past, and the participants were “followed” forward in time until 1980. Researchers used data collected in the past to define the exposure of interest: height and weight. The time when these measures were collected was set as the start of the study. The study population was defined on the basis of exposure (for example: normal BMI vs. high BMI) and followed for the development of the outcome (coronary heart disease).

Question 20

A random sample of middle-aged sedentary women were selected from four census tracts, and each subject was examined for evidence of osteoporosis. Those found to have the disease were excluded. All others were randomly assigned to either an exercise group, which followed a two-year program of systematic exercise, or a control group, which received general physical activity counseling, but no exercise program. Both groups were observed semi-annually for incidence of osteoporosis. What study design would be the best to address this scenario?

Answer 20

A randomized controlled trial is described here. Researchers were interested in testing the effectiveness of a two-year exercise program (the exposure of interest) on the development of osteoporosis (the outcome of interest). An RCT is well-suited to evaluating this relationship: the follow-up time is not too long and the exposure is of low-risk to the participants. An RCT offers a higher level of evidence than other study designs.

Question 21

Fifteen hundred adult men who worked for Lockheed Aircraft were initially examined in 1951 and were classified by diagnostic criteria for coronary artery disease. Every three years they have been reexamined for new cases of the disease; incidence rates in different subgroups have been computed annually. What study design would be the best to address this scenario?

Answer 21

This is a description of a prospective cohort study. In a prospective cohort study, researchers start with a group of people at some set point and then follow them into the future, often collecting data at set time points. In this example, an exposure of interest has not been specifically defined. However, a group (a cohort) of people are being followed forward in time to look at disease incidence.

Question 22

The local Health Department (HD) was notified of an unusual number of people presenting to the Emergency Department with severe gastrointestinal symptoms. Physicians caring for these patients reported that many of these patients mentioned eating at a local restaurant recently. To determine the possible cause of the symptoms, HD staff identified a group of people with symptoms and a group of people without symptoms. Then, people in both groups were asked about their food consumption in the past 48 hours. What study design would be the best to address this scenario?

Answer 22

The study design presented here is for a case-control study. This study design is classically used in investigations of foodborne outbreaks. This study design allows for the rapid identification of possible exposures. Cases are usually identified through medical offices (outpatient, emergency department, inpatients) as a result of a cluster being identified by medical personnel. Controls are selected to be as similar to cases as possible, then both groups are asked about possible exposures.

Question 23

The entire population of a given community is screened using colonoscopy, and all who are judged free of bowel polyps are questioned extensively about their diet. These people are then followed for several years to see whether their eating habits will predict their risk of developing bowel polyps. What study design would be the best to address this scenario?

Answer 23

A prospective cohort study is a study design with forward directionality. In a prospective cohort, the study begins at some set time point, when study participants are actively assessed for study eligibility and baseline data are collected. Then, study participants are followed into the future. The study population is defined on the basis of exposure status and followed forward in time to watch for the development of the outcome. In this example, the exposure of interest is diet type. In a typical cohort study, the population is also outcome-free at baseline (no bowel polyps). This ensures that any outcomes observed during follow-up are new outcomes (incident bowel polyps).