EBM Flashcards
Give an example of a patient oriented outcome.
Quality of life stuff
External validity means
How you can apply the study in the real world. For example, a surgery study has no external validity for a psychiatry practice
What is internal validity?
Was the study you conducted valid?
Odds ratio limits
2x2 table
Odds ratios are the cross products
OR>1 means increased risk of said outcome, good or bad
Can you calculate an ARR from an odds ratio?
No
Can likelihood ratios be applied to different populations of patients?
YES because a LR takes into account all the data in the 2x2 table.
Construct a 2x2 table
Sick Not sick
Test + a b
Test - c d
An easy way to calculate a negative LR:
1/LR = -LR
sPIN means:
SpPIn - in a test with a high Specificity, a Positive test rules In the diagnosis
sNOUT
SnNOut - in a test with a high Sensitivity, a Negative test rules Out the diagnosis
+LR =
Sensitivity/(1-Specificity)
-LR =
(1-sensitivity)/Specificity
The equation for sensitivity based on the 2x2 table
Sick Not sick
Test + a b
Test - c d
Sensitivity = a/(a+c) = true positives/all disease positives
The equation for specificity based on the 2x2 table
Sick Not sick
Test + a b
Test - c d
Specificity = d/(b+d) = true negatives/all disease negatives
What are LR cutoffs to remember?
+LR > 5 is good
+LR .2 not good
-LR
List and identify the important validity concepts for articles about therapy:
- randomization
- allocation concealment
- blinding
- intervention
- outcome assessment
- withdrawals and followup
- similarity of comparison groups and statistical adjustment as needed
- power analysis
- intention to treat analysis
T/F: A trial comparing a new anti-hypertensive medication to an older anti-hypertensive medication is NOT a valid therapy study because it does not include a placebo.
False
Examine the following abstract, paying particular attention to the outcomes studied.
Glucose Control and Vascular Complications in Veterans with Type 2 Diabetes
Duckworth W, et al.
ABSTRACT
Background The effects of intensive glucose control on cardiovascular events in patients with long-standing type 2 diabetes mellitus remain uncertain.
Methods We randomly assigned 1791 military veterans (mean age, 60.4 years) who had a suboptimal response to therapy for type 2 diabetes to receive either intensive or standard glucose control. Other cardiovascular risk factors were treated uniformly. The mean number of years since the diagnosis of diabetes was 11.5, and 40% of the patients had already had a cardiovascular event. The goal in the intensive-therapy group was an absolute reduction of 1.5 percentage points in the glycated hemoglobin level, as compared with the standard-therapy group. The primary outcome was the time from randomization to the first occurrence of a major cardiovascular event, a composite of myocardial infarction, stroke, death from cardiovascular causes, congestive heart failure, surgery for vascular disease, inoperable coronary disease, and amputation for ischemic gangrene.
Results The median follow-up was 5.6 years. Median glycated hemoglobin levels were 8.4% in the standard-therapy group and 6.9% in the intensive-therapy group. The primary outcome occurred in 264 patients in the standard-therapy group and 235 patients in the intensive-therapy group (hazard ratio in the intensive-therapy group, 0.88; 95% confidence interval [CI], 0.74 to 1.05; P=0.14). There was no significant difference between the two groups in any component of the primary outcome or in the rate of death from any cause (hazard ratio, 1.07; 95% CI, 0.81 to 1.42; P=0.62). No differences between the two groups were observed for microvascular complications. The rates of adverse events, predominantly hypoglycemia, were 17.6% in the standard-therapy group and 24.1% in the intensive-therapy group.
Conclusions Intensive glucose control in patients with poorly controlled type 2 diabetes had no significant effect on the rates of major cardiovascular events, death, or microvascular complications. (ClinicalTrials.gov number, NCT00032487 [ClinicalTrials.gov] .)
Volume 360:129-139 January 8, 2009 Number 2
The outcome “median glycated hemoglobin level” is:
A. DOE - A disease-oriented outcome
B. POE - A patient-oriented outcome
DOE - A disease-oriented outcome
Randomization is:
the best way to “allocate” subjects in your study to the comparison groups. There are right and wrong ways to conduct randomization, but in general a random number table or computer-generated randomization are the best ways.
What is allocation concealment?
Allocation concealment is not intervention “blinding”. Instead, point is to ensure that the person recruiting for the study (the person who invites people into the study, applies the inclusion and exclusion criteria and consents them for the study) does not know the group into which the subject will be placed.
Examples of continuous data in a study:
For continuous data, you’ll see means with their standard deviations, and you’ll see medians with interquartile ranges (similar to standard deviations)
Examples of categorical data in a study:
For categorical data, you’ll may see confidence intervals around the percentages
Number Needed to Treat Means:
Number Needed to Treat is a way to think about the effectiveness of a therapy as a clinician with a panel of patients.
An example:
CER = 20%, EER - 10% (the outcome is a bad outcome)
then ARD = 10% or 0.10 - there is a 10% reduction in the bad outcome for the intervention group.
therefore, the NNT = 1/0.10 = 10. We’d need to treat 10 people before we prevent an additional bad outcome.
Do not use means to calculate NNT. Use ratios.
NNT =
1/ARR or 1/ARD (ARR and ARD are the same thing)
the absolute risk reduction, risk difference or excess risk is the change in risk of a given activity or treatment in relation to a control activity or treatment
