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(PA School) Evidence Based Medicine > Lecture 8 (summary lecture) > Flashcards

Lecture 8 (summary lecture) Flashcards

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1
Q

What are the 6 components of a scientific research question?

A

1) Population
2) Intervention
3) Comparator
-ex: placebo, treatment, usual care
4) Outcomes
-ex: clinical, economic, humanistic
5) Timing
6) Setting

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2
Q

What is the gold standard for experimental research design if you want to show cause and effect?

A

Randomized control trials (RCT)

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3
Q

Give 2 examples of types of observational studies that illustrate associations between specific variables

A

Cohort or cross-sectional studies

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4
Q

Give 2 examples of research design

A

Observational vs experimental

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5
Q

Research oversight: IRB and monitoring board should be _______________ from investigators

A

independent

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6
Q

Differentiate between the roles of the IRB and Data and Safety Monitoring Board

A

1) IRB = Ethics + Study protocol review
2) Data and Safety Monitoring Board = Reviews trends of unblinded or study arm of trials

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7
Q

Define informed consent

A

Ongoing dialogue intended to provide sufficient information so that the individual can make his/her own decision about research participation

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8
Q

Informed consent:
Persons with diminished ____________ require special safeguards to prevent their exploitation in research

A

autonomy

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9
Q

Pediatric patients can _________ to treatment, but cannot consent to treatment

A

assent

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10
Q

True or false: Research design must confer internal and external validity

A

True

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11
Q

Define internal validity

A

Reflects the extent to which the clinical outcome of interest (dependent variable) in a study is caused by the treatment (independent variable)

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12
Q

1) ____________ variable = clinical outcome
2) ____________ variable = treatment

A

1) Dependent
2) Independent

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13
Q

Define external validity

A

The extent to which the results of a study can be generalized to other settings

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14
Q

Randomized controlled trials (RCTs)
Because of randomization, all observed as well as unobserved baseline characteristics are distributed evenly among the experimental and control groups, which thereby alleviates the systematic differences among participants in influencing study results.

What does this imply?

A

randomization increases internal validity of RCTs.

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15
Q

True or false: Since RCTs are conducted in tightly controlled clinical settings, the results may not be generalizable to routine (real-world) settings.

A

True

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16
Q

Observational studies:
Define cohort studies

A

two groups, the exposed and the unexposed, are followed (prospectively or retrospectively) over a period of time until the development of outcome of interest

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17
Q

Observational studies:
Define case-control studies and give an example

A

Comparison of exposure status among individuals with the disease or outcome of interest (cases) and those without the disease or outcome (controls)
-Example: Patients with squamous cell carcinoma; Who smoked?

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18
Q

Observational studies:
What has the highest level of observational evidence?

A

Cohort studies

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19
Q

Observational studies:
1) What are two types of cohort studies?
2) Give an example of cohort studies

A

1) Prospective or retrospective
2) Example: Smokers vs. non-smokers; Who develops squamous cell carcinoma?

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20
Q

Observational studies: Define cross-sectional and give an example

A

Prevalence studies; exposure and outcome of interest are measured at the same point in time
-Example: How many people were infected with COVID-19 and died during 2020?

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21
Q

Observational studies: Define case series and give some well-known examples

A

1) Collection of case reports
2) Credited with the discovery of AIDS and identification of the relationship between thalidomide and birth defects

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22
Q

Observational studies: Define case report. What is unique about this?

A

1) Single patient with novel predicament
2) Lowest level of observational evidence

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23
Q

What observational study has the lowest level of observational evidence?

A

Case report studies

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24
Q

What studies maximize validity and minimize bias?

A

RCTs

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25
RCTs: 1) ___________ validity is maximized by having a control group and randomizing all participants 2) Bias can significantly decrease __________ validity
1) Internal 2) internal
26
_____ occurs when the estimate of the effect of the exposure on disease does not represent the true effect of the exposure on the disease outcome
Bias
27
Describe selection bias
1) Error in the estimate of effect due to procedures used to select subjects, or factors that influence study participation or follow-up 2) In cohort studies, selection bias is less likely to occur than in case-control studies because selection of subjects into the cohort usually occurs before the disease occurs 3) Preferential enrollment of specific patients into one treatment group over another 4) Baseline demographics between control and experimental group should be comparable 5) Patients must have equal probabilities to be allocated to the treatment or control arm
28
What occurs when the exposure affects the detection of the disease (or outcome)? What does this lead to?
Detection bias; systematic differences between groups in how outcomes are determined
29
Define diagnosis bias
Exposure affects the diagnosis and hence the selection of cases in a case-control study
30
What type of bias occurs when errors in the measurement or collection of data biases the estimate of effect?
Information bias
31
What type of bias occurs when the accurate measurement of the disease depends on the exposure and results in a biased estimate of effect?
Differential misclassification bias
32
Define recall bias
Occurs when cases are more likely to recall the true level of a previous exposure compared to controls
33
Nondifferential misclassification bias: 1) Define this term 2) What data sources can be more prone to this type of bias?
1) Occurs when the misclassification of the disease is the same for all categories of the exposure or the misclassification of the exposure is the same for all categories of the disease 2) Secondary data sources
34
External events that occur during the course of the study (e.g., death of a family member or losing a job) are defined as what kind of bias?
History bias
35
Normal changes in study participants over time is referred to as what kind of bias?
Maturation bias
36
Define attrition bias
Differential dropout of patients from the treatment and/or control groups
37
Define testing bias
Studies that require participants to take tests or participate in their own assessment repeatedly over time are susceptible to problems with internal validity due to potential improvements that can occur simply by repeated testing
38
Define instrumentation bias
Changes in the sensitivity of the instrument, improvements in technology, and changes in the measurement techniques over time
39
What type of bias is defined as a "phenomenon where initial measurements of a variable are extremely different, either higher or lower, from the population mean, but then subsequent measurements are closer to the average"?
Regression to the mean
40
Define investigator bias
Errors in study design, implementation, or analysis by the investigator
41
Define Ascertainment bias
Effects of intervention can be exaggerated if the investigators choose only those time points where the measured outcomes show the most benefit for the intervention, and ignore the data showing less impact of the intervention on outcomes
42
Define simple randomization. What can it lead to?
Random number generator to allocate participants Can lead to treatment arms having unequal numbers of test subjects
43
Define block randomization and what it leads to
Total number of subjects to be enrolled in the study is divided into a series of “blocks” Arms will have comparable number of participants
44
Define stratified randomization. When may it not be required?
Process of ensuring certain baseline characteristics are equal between the groups of a study Patients are divided into different strata and then randomized using blocks In very large trials, stratification may not be required
45
Define group or cluster randomization
Group of subjects are selected for randomization
46
___________________________ occurs when those enrolling patients into the study are prevented from knowing which group the patients are allocated the study
Allocation concealment
47
Allocation Concealment: 1) Decreases risk of what? 2) When does it occur?
1) Selection bias 2) Prior to the patients being enrolled in the study and stops once they are enrolled
48
Blinding: Define open-label
No blinding Potential for patient reporting and investigator bias May see open label in Phase 1 drug trials
49
Define single-blind
Only one set of individuals is unaware of what the patients are receiving
50
Define double blind
Two sets of individuals are unaware of what the patients are receiving
51
Define triple blind
Patients, providers and data analysist are all blinded
52
Define double-dummy and give an example
1) More than one placebo is used to help the treatments look the same in all the groups 2) Non-inferiority drug trial comparing two drug formulations of the same triptan and its efficacy Comparing sumatriptan PO vs. sumatriptan SUBQ Arm 1: Sumatriptan PO and placebo SUBQ Arm 2: Placebo PO and sumatriptan SUBQ
53
Sample size: What is the goal?
Goal is to determine the appropriate number of subjects that are needed to test the primary study hypothesis
54
Analysis 1) Define relative risk 2) Define relative risk difference or relative risk reduction
1) Ratio between the rate of the outcome in the treatment and control groups 2) Comparison of risk between treatment vs. control
55
Analysis: 1) Define absolute risk difference 2) Define NNT
1) Net benefit beyond control group observation 2) Refers to the number of patients that must receive the treatment in order to for one patient to experience a desired outcome -Preferably a low number -Round up to avoid overstating effect
56
Analysis: Define NNH
Reflects the numbers of patients that must receive the treatment in order to for one patient to experience an adverse outcome Preferably a high number
57
Define NNH
Number of patients receiving treatment for a specific period of time that will have an adverse effect (harm) NNH = 1 / ARR Can use absolute value Round down to avoid understating potential harm
58
What is the equation for: 1) RR 2) RRR 3) ARR 4) NNT
1) RR = [ A/(A+B) ] / [ C / (C +D) ] 2) RRR = 1 - [ A/(A+B) ] / [ C / (C +D) ] RRR = ARR / [ C / (C +D) ] 3) Control group rate = C / (C +D) Experimental group rate = A / (A+B) ARR = experimental group rate – control group rate 4) NNT = 1 / ARR
59
Cross-sectional studies: Explain response rate
60% response rate is considered a good benchmark in determining adequate survey response Johnson TP, Wislar JS. Response rates and nonresponse errors in ­surveys. JAMA. 2012;307(17):1805–1806. [PubMed: 22550194] Poor response rates limit generalizabilit
60
Differentiate incidence and prevalence
1) Incidence – measures the risk of developing an outcome 2) Prevalence – measures the probability of having an outcome More appropriate to say “point prevalence” compared to “prevalence rate” since this is a proportion and not a rate
61
How do you truly identify patients that have an outcome (true positive) and avoid detection of an outcome in patients that do not have it (false positive)?
Sensitivity and specificity
62
Most tests used to diagnose diseases have a sensitivity of _______% and specificity of _________%
80% and specificity of 90%
63
Most tests used to diagnose diseases have a sensitivity of 80% and specificity of 90%; explain
Sensitivity is gained at the expense of specificity and vice versa Receiver operating characteristic curves further define this tradeoff
64
What is the Central limit theorem?
The mean of all sample means will equal the population mean The standard deviation of the sampled means is equal to the standard error of the mean As the sample size increases, the distribution of the sample means will approach a normal distribution regardless of the underlying distribution of the variable
65
What makes a good hypothesis?
Declarative Describes a relationship between two or more variables
66
What is the Null hypothesis (HO)
1) No relationship or no difference between the variables of interest 2) Conclusions of studies are made with respect to the null hypothesis Reject Fail to reject
67
Explain confidence intervals
No difference between variables = 1 If the interval contains the null value of interest, then the null hypothesis is not rejected at a given significance level If the interval does not contain the null value, the null is rejected at a given significance level
68
Bivariate Analysis: Differentiate the independent and dependent variables
Independent variable is discrete (nominal) Standards of care Standards of care + exercise Dependent variable is continuous (ratio)
69
Bivariate analysis: What should you use?
Use nondirectional statistical test Null hypothesis says there is no difference between groups Preferred test is independent groups t-test; tests the differences in the means of two groups

(PA School) Evidence Based Medicine (18 decks)

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