EBM Flashcards
Categories of evidence
Level A: Good scientific evidence suggests that the benefits of the clinical service substantially outweigh the potential risks. Clinicians should discuss the service with eligible patients.
Level B: At least fair scientific evidence suggests that the benefits of the clinical service outweighs the potential risks. Clinicians should discuss the service with eligible patients.
Level C: At least fair scientific evidence suggests that there are benefits provided by the clinical service, but the balance between benefits and risks are too close for making general recommendations. Clinicians need not offer it unless there are individual considerations.
Level D: At least fair scientific evidence suggests that the risks of the clinical service outweighs potential benefits. Clinicians should not routinely offer the service to asymptomatic patients.
Level I: Scientific evidence is lacking, of poor quality, or conflicting, such that the risk versus benefit balance cannot be assessed. Clinicians should help patients understand the uncertainty surrounding the clinical service.
Levels of evidence sources
Level I: Evidence obtained from at least one properly designed randomized controlled trial.
Level II-1: Evidence obtained from well-designed controlled trials without randomization.
Level II-2: Evidence obtained from well-designed cohort or case-control analytic studies, preferably from more than one center or research group.
Level II-3: Evidence obtained from multiple time series with or without the intervention. Dramatic results in uncontrolled trials might also be regarded as this type of evidence.
Level III: Opinions of respected authorities, based on clinical experience, descriptive studies, or reports of expert committees.
Levels of evidence and grades of recommendations
Levels of Evidence:
IA
Evidence from meta-analysis of randomized controlled trials
IB
Evidence from at least one randomized controlled trial
IIA
Evidence from at least one controlled study without randomization
IIB
Evidence from at least one other type of quasi-experimental study
III
Evidence from non-experimental descriptive studies, such as comparative studies, correlation studies, and case-control studies
IV
Evidence from expert committee reports or opinions or clinical experience of respected authorities, or both
Grades of Recommendations:
A
Directly based on Level I evidence
B Directly based on Level II evidence or extrapolated recommendations from Level I evidence
C Directly based on Level III evidence or extrapolated recommendations from Level I or II evidence
D Directly based on Level IV evidence or extrapolated recommendations from Level I, II, or III evidence
Requirements fir screening test
• Prevalence of disease must be sufficiently high. • Disease must have significant morbidity and mortality rates. • Effective treatment must be available. • Improved outcomes from early diagnosis and treatment must be present. • Test should have good sensitivity and specificity parameters. • Test should carry acceptable risks and be cost-effective
Definitions of specificity, sensitivity, ppv and npv
Test Result Disease Present Disease Absent Positive True positive ( a ) False positive ( b ) Negative False negative ( c ) True negative ( d )
Positive predictive value (true-positive rate) = a /( a + b ).
Negative predictive value (false-positive rate) = d /( c + d ).
Sensitivity = a /( a + c ); patients with the disease who have a positive test.
Specificity = d /( b + d ); patients without the disease who have a negative test.
Definitions positive and negative likelihood ratios
A high positive likelihood ratio indicates a high likelihood of the presence of disease, whereas a high negative likelihood ratio identifies the absence of disease.
Positive likelihood ratio: = Sensitivity ( probability that test is positive in diseased patients )/ 1 − Specificity ( probability that test is positive in nondiseased patients )
Negative likelihood ratio: = 1 /1 − Sensitivity ( probability that test is negative in diseased d patients ) − Specificity ( probability that test is negative in nondiseased patients )
RRR definition
RRR=Incidence of outcome in control group − Incidence of outcome in study group /Incidence of outcome in control group
ARR definition
ARR=Incidence of outcome in control group − Incidence of outcome in study group Incidence of outcome in control group
NNT definition
NNT represents the number of patients who need to be treated to prevent a single outcome event and is the inverse of the ARR (i.e., 1/[ X − Y ]).
