HS 2801 Research Methods Week 7
quasi-experimental design
An experimental study that assigns participants to an intervention or control group using a nonrandom method.
______ is an evaluation of the cost-effectiveness of an intervention that is based on both its effectiveness and resource considerations.
Efficiency
The _______, or true positive rate, is the proportion of people who actually have a disease (according to the reference standard) who test positive using the new test.
sensitivity
Allocation Bias
A form of bias that occurs as a result of nonrandom assignment of participants to experimental study groups.
Detection Bias
A form of bias that occurs when a population group that is routinely screened for adverse health conditions incorrectly appears to have a higher-than-typical rate of disease because more frequent testing enables a higher case detection rate in that population than in the general population; also called surveillance bias.
Reporting bias
A form of bias that occurs when members of one study group systematically underreport or overrerport an exposure or outcome.
Standard of care
An existing therapy (such as the best therapy currently available or the therapy that is used most often in the location where the study is being conducted) that is used as a comparison for a new therapy being experimentally tested.
Factorial design
An experimental design that tests several different interventions in various combinations within one trial.
Crossover Design
An experimental study design in which each participant serves as his or her own control; some participants are assigned to receive the active intervention first and then the control, and others are assigned to receive the control first and then the active intervention.
The number needed to harm (NNH) is the number of people who would need to receive a particular treatment in order to expect that one of those people would have a particular _____ outcome. A large NNH indicates a safer intervention. NNT and NNH are often used for cost-effectiveness analysis.
adverse
The_____- (AUC) is an aggregate measure of how well a screening or diagnostic test performs across various cutoff points. AUC values can range from 0 to 1, with 0 indicating a test that is incorrect 100% of the time and 1 indicating a test that is correct 100% of the time.
area under the curve
The term _____ describes the treatment and nontreatment groups of an experiment
arms
A treatment-_______ analysis (or intention-to-treat analysis) includes all participants, even if they were not fully compliant with their assigned protocol. Treatment-assigned analysis is better at measuring real-world (rather than ideal-world) effectiveness.
assigned
When there are ethical concerns about withholding a potentially lifesaving intervention from some participants, it may be possible for participants to serve as their own controls. A____________ study is a nonrandomized experimental study that measures the same individuals before and after an intervention so that each participant's "before" status can serve as that individual's control.
before-and-after
The principles of _______ and nonmaleficence require that researchers balance the likely benefits and risks of the study.
beneficence
Experimental studies are the gold standard for assessing _______-
causality used for clinical trials of new therapies for individuals with various illnesses, field trials of preventive interventions like vaccinations, and community trials of public health and environmental interventions.
Experimental studies use many of the same measures of association that ____ studies do, including rate ratios, attributable risks (excess risk or risk reduction), attributable risk percentages, measures of survival, and various types of regression models.
cohort Cohort studies use these measures to examine the impact of an unassigned exposure on the incidence of disease. Experimental studies use the statistics to quantify the impact of an assigned exposure on the likelihood of having a favorable or an unfavorable outcome
The _____ accuracy is the percentage of individuals who are correctly classified by the test as true positives or true negatives (that is, the percentage for which both the reference test and the new test yield the same result). An ideal test will have 100% diagnostic accuracy.
diagnostic The sensitivity, specificity, positive predictive value, and negative predictive value of a new screening or diagnostic test in comparison to a reference standard are other metrics of how well the test performs
The principle of ____- justice necessitates that the source population be an appropriate one and that the research study not exploit individuals from populations that are unlikely to have continued access to the therapy if it is found to be successful.
distributive
In a ____- experimental study, neither the participants nor the researchers assessing the participants' health status know which participants are in an active or control group.
double-blind
The principle of ________ states that experimental research should be conducted only when there is genuine uncertainty about which treatment will work better.
equipoise
An _____- trial aims to demonstrate that a new intervention is as good as some type of comparison
equivalence
Experimental studies also require careful consideration of the ________- challenges associated with assigning participants to an exposure, even if that exposure is expected to improve health status.
ethical
An adverse _______ is a negative outcome that may be the direct result of a study-related exposure or may be a coincidental occurrence that is not directly related to the study but happens after an individual receives a study-related exposure
event
An _________ study assigns participants to intervention and control groups in order to test whether an intervention causes an intended outcome.
experimental
In experimental studies, because the researcher assigns participants to receive a particular _________, the exact dose, duration, and frequency of the exposure are known. The researcher knows when the exposure occurred, so the health status of each participant before and after the exposure can be compared. The researcher can therefore assess whether the exposure may have caused a particular outcome.
exposure
Blinding is intended to minimize ____________ bias, bias in an epidemiological study that arises due to systematic measurement error.
information There are many types of information bias, such as recall bias, reporting bias, detection bias, and observer bias.
An __________ is a strategic action intended to improve individual and/or population health status.
intervention
The first step in an experimental study is to carefully define the ___________ that participants assigned to the active intervention group will receive and to decide on the person, place, and time (PPT) criteria for the study.
intervention
Experimental medical studies typically focus on testing the effectiveness of ______ intended to diagnose, treat, cure, or prevent adverse health conditions.
interventions
One commonly used type of control is a ________, an inactive comparison that is similar to the therapy being tested.
placebo
Experimental public health studies typically focus on testing the effectiveness of interventions designed to prevent health problems at the _________ level.
population
The __________ predictive value (PPV) is the proportion of people who test positive with the new test who actually have the disease (according to the reference standard).
positive
The false ____ rate is the proportion of people who actually do not have a disease (according to the reference standard) who incorrectly test positive using the new test. The false positive rate can also be calculated as 1 - specificity (that is, the number one minus the specificity, which must fall between 0 and 1).
positive
The____________ratio (LR+) test examines whether a new test is good at predicting the presence of disease. The LR+ is calculated as the probability that an individual with the disease has a positive test divided by the probability that an individual without the disease has a positive test.
positive likelihood A larger LR+ (such as LR > 10) indicates a good test.
A ________ standard is the test used for comparison when examining the validity of a new screening or diagnostic test. For example, a new blood antigen test for a type of cancer might be compared to biopsy results. In this scenario, a biopsy is considered to be a "gold standard" because the test shows the actual presence of disease in affected people.
reference
The principle of ___- for persons requires that all participants volunteer for a study without being unduly influenced by the prospect of being compensated for their participation. Respect also requires that all participants understand what it means to be a research subject, including the possibility of being assigned to a control group instead of the new intervention.
respect
The goal of most studies of new or improved ______ or diagnostic tests is to compare two assessments that are supposed to measure the same thing. In most situations, this goal involves comparing a new test to an existing one.
screening
Blinding is usually possible only when all participants are assigned to __________ exposures. If participants in both the active intervention group and the control group are taking pills (of the same color, shape, size, and taste) or if both are getting injections, a blinded study may be possible.
similar
The number needed to treat (NNT) is the expected number of people who would have to receive a treatment to prevent an ________ outcome in one of those people (or, alternately stated, to achieve a favorable outcome in one person). A small NNT indicates a more effective intervention.
unfavorable
_____ randomization is an allocation method that randomly assigns groups of people to an intervention group and other groups of people to a control group. In this method, randomization occurs at the group rather than individual level.
Block. For example, if there were 10 elementary schools in a county, schools could be randomly assigned to be intervention or control schools. All of the students in the 5 schools randomly assigned to the intervention group would receive the intervention. All of the students in the other 5 schools would be assigned to the comparison.
____ is calculated with the same equation as efficacy but refers to results obtained under real-world, less-than-ideal conditions. For example, in a real-world setting, some participants might skip some doses of an experimental drug, or they might not take the doses at the exact specified times, or they might not store the pills at the ideal temperature
Effectiveness
___ typically refers to results under ideal circumstances, such as when an experiment is conducted in a controlled laboratory setting and all participants are fully compliant with the protocol.
Efficacy
_______ is a measure of the success of an intervention that is calculated as the proportion of individuals in the control group who experienced an unfavorable outcome but could have expected to have a favorable outcome if they had been assigned to the active group instead of the control group
Efficacy A high efficacy is an indication that an intervention is successful.
_________, sometimes called masking, is an experimental design element that keeps participants (and sometimes some members of the research team) from knowing whether a participant is in the active intervention group or the control group.
Blinding
_________ ensures that participants in the active intervention group will not report more favorable results simply because they expect a positive outcome. It also keeps assessors from intentionally or unconsciously recording more favorable results for participants in the active intervention group.
Blinding
Experimental studies sometimes include a control group of participants who are randomly assigned to maintain their usual routines, but this method is usually not preferred. The approach raises ethical concerns about discouraging the adoption of healthier lifestyles during the course of the study. It also raises concerns about the _________ effect, a type of bias that occurs when participants in a study change their behavior for the better because they know they are being observed.
Hawthorne For example, suppose a researcher is initiating a study of a new weight-loss program and plans to randomly assign participants either to the new therapy or to a usual-routine group. In this situation, simply informing the controls that they will be weighed at the start and end of the study period will be enough to spur a sizable proportion of the control group to initiate an exercise program, start eating a healthier diet, or take other steps to lose weight. These changes may interfere with the accurate measurement of the impact of the new intervention.
_________ ratio tests are probability ratios used to evaluate the accuracy of screening and diagnostic tests.
Likelihood
_________ bias occurs when an observer (a researcher) intentionally or unintentionally evaluates participants differently based on their group membership, such as systematically evaluating cases and controls in a case-control study differently.
Observer
____-controlled studies allow the effect of the active therapy to be examined separately from the boost in health status that people may experience simply by participating in a clinical trial or receiving some other intervention
Placebo
____ science is the scientific study of which preventive health interventions are effective in various populations, how successful the interventions are, and how well they can be scaled up for widespread implementation.
Prevention
______ is the assignment of participants to an exposure group in an experimental study using a chance-based method that minimizes several types of possible bias.
Randomization For example, randomization minimizes the problems that could occur if participants were able to choose the intervention or control group they preferred. Some people would prefer to know they were getting the active intervention, while others with less risk tolerance might prefer to be in a control population. Self-selection might significantly alter the results of the trial.
____ is a type of secondary prevention in which all members of a well-defined group of people are encouraged to be tested for a disease based on evidence that members of the population are at risk for the disease and early intervention improves health outcomes.
Screening
______ randomization is the use of a coin toss, a random number generator, or some other simple mechanism to randomly assign each individual in an experimental study to one of the exposure groups.
Simple
____________ randomization is the division of a population into subgroups prior to randomly but systematically assigning each individual within each subgroup to one of the exposure groups in an experimental study.
Stratified Stratified randomization is used when it is important for members of certain subpopulations to be distributed evenly across the treatment arms of a trial. For example, suppose that 75% of the volunteers for a study are female and only 25% are male. Stratified randomization can ensure that enough males are assigned to the intervention group. The list of female volunteers can be sorted into alphabetical order by last name, and then every other individual in the ordered list can be assigned to the active group. This same process can be repeated with the male volunteers. This stratified process will ensure that half of the females and half of the males are assigned to the intervention group.
A _______ trial is an experiment in which some of the participants are assigned to an intervention group and some are assigned to a nonactive comparison group.
controlled
A _____ or threshold is a value that divides a numeric variable into separate categories. For example, a systolic blood pressure of 140 mm Hg could be selected as the value that defines the presence or absence of hypertension. People with a blood pressure of 140 mm Hg or greater would be coded as having hypertension, while people with a blood pressure of less than 140 mm Hg would be coded as not having hypertension.
cutpoint
A ______ experiment is a research study in which the independent variable is not manipulated by the researcher but instead changes due to external forces.
natural. For example, a researcher may seek to understand the impact of a devastating tornado on the health of residents of the affected community by comparing residents in the damaged areas to residents of neighboring areas who were not directly harmed by the twister. The researcher does not cause the tornado or select which community it affects, but the outcomes can still be examined and compared. These are not true experimental studies because the "interventions"—a natural disaster and an infection policy change in a hospital—are not ones that can be manipulated by a researcher, but they can be evaluated using analytic methods similar to those used for true experiments.
The _______ predictive value (NPV) is the proportion of people who test negative who actually do not have the disease
negative
The false ______ rate is the proportion of people who actually have a disease who incorrectly test negative using the new test. An ideal screening or diagnostic test would have a 0% rate of false positive and false negative outcomes.
negative
The ____ likelihood ratio (LR-) test examines whether a new test is good at predicting the absence of disease. The LR- is calculated as the probability that an individual with the disease has a negative test divided by the probability that an individual without the disease has a negative test.
negative A smaller LR- (such as LR < 0.1) indicates a good test.
A ________ trial aims to demonstrate that a new intervention is no worse than some type of comparison.
noninferiority
To minimize the risk of bias in studies that are not blinded, it is helpful to identify ________ outcome measures such as laboratory tests rather than relying on ______- outcome measures such as participants' self-reported feelings.
objective, subjective
A very common experimental study design used in the health sciences is a______________ in which some participants are randomly assigned to an active intervention group, the remaining participants are assigned to a control group, and all participants from both groups are f
randomized controlled trial (RCT) RCTs and all other types of experimental study designs require careful descriptions of: The intervention The type of control that will be used and why it is appropriate How participants will be assigned to exposure groups The end point that will constitute a favorable outcome for the trial
An adverse ______ is a negative side effect of a medication, vaccination, or other exposure, or another bad outcome related to a study.
reaction
A treatment-____________ analysis of experimental data includes only the participants who were fully compliant with their assigned intervention or comparison protocol. Treatment-received analysis allows for the calculation of efficacy, because the only participants included in the analysis are those who never missed taking a pill at the prescribed time, never missed a scheduled clinical exam, and were otherwise exemplary study subjects.
received
A _______ (ROC) curve, or ROC curve, can be used to graphically examine the accuracy of a screening or diagnostic test by plotting the false positive rate (on the x-axis) versus the true positive rate (on the y-axis) for the different possible cutoff points of the test. In other words, the ROC curve plots 1 - specificity on the x-axis and sensitivity on the y-axis for a variety of cutoff points.
receiver operating characteristics
In a ________- experimental study, participants do not know whether they are in an active group or a control group
single-blind
The _______, or true negative rate, is the proportion of people who do not have the disease who test negative with the new test.
specificity
A __________- trial aims to demonstrate that a new intervention is better than some type of comparison, not merely as good as the comparison
superiority
Most experimental studies are ______ trials.
superiority
A __________ period for an experimental study is a time between arms of the study when patients receive no treatment. In a crossover study, both groups may take a break between the two arms of the experiment. This break is intended to reduce ______- effects, the residual effects from the first part of an experimental study that may bias the results of the second part of a crossover study if a sufficient washout period between the two arms of the study is not implemented. Each participant's status before the intervention is compared to his or her own status after the intervention. However, the results of crossover experimental designs may not be as clear-cut as placebo studies because time alone can lead to significant improvements or declines in health status, especially among those who are severely ill.
washout, carryover
