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MKSAP BOARD BASICS GENERAL INTERNAL MEDICINE
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MKSAP BOARD BASICS GENERAL INTERNAL MEDICINE
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MKSAP BOARD BASICS GENERAL INTERNALMEDICINE
___ is the ability of a test to detect a disease when it is truly present.
Sensitivity (true positive rate)
___ is the ability of a test to exclude disease when it is truly absent.
Specificity (false positive rate)
As the prevalence of a condition ___, the positive predictive value increases and the
negative predictive value decreases.
Prevalence increases
- changes in prevalence do not alter sensitivity or specificity but alter predictive values
A likelihood ratio (LR) is a measurement of the odds of having a disease independent of
the disease prevalence. Separate LRs are calculated for use when a test result is
positive (LR+) or negative (LR−)
equations?
LR + = sensitivity /1-specificity
LR - = (1-sensitivity)/specificity
• LR+of2,5, and 10 increase the probability of disease by approximately 15%,30%,and
45%, respectively.
• LR−of 0.5, 0.2, and 0.1 decrease the probability of disease by approximately 15%,
30%, and 45%, respectively.
The presence of the presumed risk factor and presence of the outcome are measured
at one point in time in a population.
study design?
Cross-section
Subjects are divided into groups based on the presence or absence of the outcome of
interest, and then the frequency of risk factors in each group is compared.
study design?
Retrospective (case control)
,Subjects are divided into groups based on the presence or absence of the presumed
risk factor and followed for a period of time.
At the end of the study, the frequency of the outcome is compared.
study design?
Prospective (cohort)
Subjects are randomly divided into groups; one group receives the intervention (patients
and researchers may be blinded to treatment, termed double-blind) and followed
forward in time.
At the end of the study, the frequency of the outcome is compared.
This study design reduces the effect of unmeasured (confounding) variables that may
influence outcomes of a study.
study design?
Randomized controlled trial
Usually, multiple clinical trials using similar randomization techniques and interventions
can be combined into one large analysis to address very precise clinical questions.
The results may be analyzed using the technique of meta-analysis, in which all trial
results are combined to create a single point estimate.
study design?
Systematic review with meta-analysis
Strength of research designs in descending order (strongest to weakest)
1. RCT including systematic reviews of RCTs
2. RCT without randomization
3. Case-control or cohort study
4. Evidence using many points in time, with or without intervention
5. Evidence based on experience, descriptive studies, or expert opinion
Definition of absolute risk (AR).
Calculation.
The probability of an event occurring in a group during a specified time period
AR = patients with event in group / total patients in group
,Also known as event rate. Often, an experimental event rate (EER) is compared with a
control even rate (CER)
Definition of relative risk (RR)
calculation.
The ratio of the probability of developing a disease with a risk factor present to the
probability of developing the disease without risk factor presents
RR = EER/CER
EER - experimental event rate
CER - control event rate
Used in cohort studies and RCTs
Absolute risk reduction (ARR) definition
calculation
The absolute difference in rates of events between experimental group and control
group
ARR = |EER−CER|
EER - experimental event rate
CER - control event rate
Relative risk reduction (RRR) definition
calculation
The ratio of ARR to event rate among controls
RRR = | EER − CER | / CER
EER - experimental event rate
CER - control event rate
For very infrequent events, RR can be large while AR is small
Number needed to treat (NNT) definition
calculation
, Number of patients needed to receive a treatment for one additional patient to benefit
NNT=1/ARR
A good estimate of the effect size in easy-to-understand terms for patients
Number needed to harm (NNH) definition
calculation
Number of patients needed to receive a treatment for one additional patient to be
harmed
NNH = 1/ARR
___ provides boundaries within which exists a high probability (95% by convention) of
finding the "true" value. For example, if the measured mean difference between two
groups is 2.4, and the 95% ___ is 1.9 to 3.0, the probability that the true value lies
between 1.9 and 3.0 is 95%.
Confidence interval (CI)
When used in association with RR, if the CI includes the number __ , no risk or benefit
exists; the outcomes for the control and experimental groups are the same.
number 1
The P value indicates the likelihood of the study result being caused by chance alone.
A P value of less than ___ represents a 1
in 20 chance of obtaining the observed results by chance.
0.05
A ____ is incorrectly concluding that a statistically significant difference exists between
the experimental and control groups. If the study's P value is <0.05, then a <5% chance
exists that a type I error has occurred.
type I error
A ___ is incorrectly concluding no difference exists between the experimental and
control groups. Studies with small numbers of subjects may not have the statistical
"power" to detect true differences between groups and may be subject to type __ errors.
type II error
ACIP recommendation for influenza.
One dose annually (for all persons ≥18 y), including pregnant women and those with
HIV infection
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