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350 Section 20: Rare Vascular Entities
11. RATIONALE
Covered stents (self-expanding) for exclusion of popliteal artery aneurysms are a safe and effective alternative to open surgical repair in high-risk patients. The Supera stent, because of its
interwoven nitinol design, is useful in treating popliteal artery occlusive lesions. For vein graft
stenosis behind the knee, a covered stent (Viabahn WL Gore) 6 mm in diameter was deployed
following preangioplasty then followed by postangioplasty, and this was deemed preferable
to repeat open repair. In this patient, a covered stent has remained patent for the past 10 years
without requiring any secondary operation.
Correct Answer B Self-expanding covered stent
Reference
Hans, S. S. (2020). Management of a patient with complicated adventitial cystic disease of the popli-
teal arter y in challenging arterial reconstructions. In S. S. Hans (Ed.), Challenging arterial recon-
structions: 100 clinical cases (pp. 259–262). Cham, Switzerland: Springer Nature Switzerland AG.
12. RATIONALE
From the French Takayasu Network, a retrospective multicenter study of characteristics
and outcomes of 318 patients with Takayasu arteritis (TA) fulfilling American College of
Rheumatology and Ishikawa criteria were analyzed. The median age at the time of diagnosis was 36 (25–47 years) and 276 (86.8%) were women. After a median follow-up of 6.1 years,
relapses were observed in 43%, vascular complications in 38%, and death in 5%. A progressive
clinical course was observed in 45%, carotidynia in 10%, and retinopathy in 4%. The 5-and10-year event-free survival, relapse-free survival, and complication-free survival were 48.2%
and 36.4%, 58.6% and 47.7%, and 69.9% and 53.7%, respectively. Progressive disease course
(p = 0.018) and carotidynia (p = 0.036) were independently associated with event-free survival.
Male sex (p = 0.048) and elevated C-reactive protein (p = 0.013) and carotidynia (p = 0.003) were
associated with relapse-free survival. Progressive disease course (p = 0.017), thoracic aortic
involvement (p = 0.009), and retinopathy (p = 0.002) were associated with complication-free
survival. This nationwide study showed that 50% of patients with TA will relapse and will experience a vascular complication ≤10 years from diagnosis.
Correct Answer C 38% of patients
Reference
Comarmond, C., Biard, L., Lambert, M., et al. (2017). Long-term outcomes and prognostic factors of
complications in Takayasu arteritis: a multicenter study of 318 patients. Circulation, 136(1 2),
1114–1122. PMID: 28701469
13. RATIONALE
The basic pathologic features of TA are mural changes in the great vessels. Mural changes
are often not satisfactorily evaluated by conventional angiography. Diagnosis during the
early stage is often missed or delayed because of a non-specific clinical presentation and no
luminal changes in the aorta or its branches but detectible by conventional arteriography,
which often underestimates the extent of true disease extent even in a pulseless disease
state. Among 85 patients undergoing carotid bifurcation to iliac bifurcation CTA, 81 (95%)
had aortic involvement without or with aortic arch involvement; the left common carotid
artery and left subclavian artery were most commonly involved: 77% and 76%, respectively.
Section 20: Rare Vascular Entities 351
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The extent of disease assessed by mural changes was more extensive than that assessed
by luminal changes in 52 (61%) patients. Arterial involvement was contiguous in 69 (81%)
patients, and skipped lesions were identified in 16 (19%) patients. An analysis of mural
findings revealed the coexistence of active and inactive lesions in 11% of patients. CT scans
should be performed from the carotid bifurcation to the iliac bifurcation in order to adequately evaluate, diagnose, and manage TA.
Correct Answer C CTA
Reference
Chung, J. W., Kim, H. C., Choi, Y. H., et al. (2007). Patterns of aortic involvement in Takayasu arteritis
and its clinical implications: evaluation with spiral computed tomography angiography. J Vasc
Surg, 45(5), 906–914. PMID: 17466787
14. RATIONALE
The patient’s young age with angiographic findings are highly suggestive of mid-aortic syndrome cause by Takayasu arteritis. She should undergo CTA from carotid bifurcation to
common femoral arteries. The patient should have genetic testing as well as blood tests for
inf lammatory markers such as C-reactive protein and sedimentation rate. The angiography
is not consistent with the diagnosis of premature atherosclerotic disease, which can affect
younger women from 30 to 40 years of age with a history of significant nicotine abuse, hypertension, and premature ovarian failure (menopause). The disease affects the distal aorta and proximal common iliac arteries, which are small in caliber. Inferior vena cava compression from a
large retroperitoneal tumor may occur, but arterial occlusion from a retroperitoneal mass is
extremely unlikely. Marfan syndrome usually causes ascending aortic aneurysm and may also
cause an aneurysm in the aortic arch, descending thoracic, and abdominal aorta but is not a
common cause of infrarenal aortic stenosis.
Correct Answer C Mid-aortic syndrome caused by Takayasu arteritis (TA)
Reference
Delis, K. T., & Gloviczki, P. (2005). Middle aortic syndrome: from presentation to contemporary open
surgical and endovascular treatment. Perspect Vasc Surg Endovasc Ther, 17(3), 187–203. PMID:
16273154
15. RATIONALE
The aim of treatment is to improve symptoms of intermittent claudication, reverse hypertension, and improve perfusion to the renal parenchyma and bowel. Medical control of hypertension and use of corticosteroids and immunosuppressive drugs is essential in the acute phase
of the disease prior to surgical intervention. Balloon angioplasty of an aorta or covered stent is
not indicated for mid-aortic syndrome. Patch angioplasty of the aorta can be considered in a
shorter segment of involvement in mid-aortic syndrome. In most patients, aorto-aortic bypass,
preferably using a left retroperitoneal approach through the eighth intercostal space, provides
excellent exposure. Proximal anastomosis is performed to the supraceliac aorta and distal anastomosis to the distal aorta above its bifurcation. PTFE grafts are preferable to Dacron grafts, as
the latter undergo aneurysmal dilatation over a period of years. Aortic bypass for mid-aortic
syndrome is safe with an excellent long-term patency. The patient did not require renal artery
reconstruction because of normal renal arteries.
352 Section 20: Rare Vascular Entities
Correct Answer D Supraceliac aorta to distal abdominal aorta bypass graft using left flank
retroperitoneal approach through the eighth ICS
Reference
Delis, K. T., & Gloviczki, P. (2005). Middle aortic syndrome: from presentation to contemporary open
surgical and endovascular treatment. Perspect Vasc Surg Endovasc Ther, 17(3), 187–203. PMID:
16273154
16. RATIONALE
Buerger disease or segmental thromboangiitis obliterans (TAO) is a non-atherosclerotic
inf lammatory arteritis that involves small- to medium-size arteries and veins of the extremities. Exposure to tobacco is central to the initiation, maintenance, and progression of TAO.
The annual incidence of TAO is reported to be 12.6% per 100,000 in the United States and is
much greater in the Middle East and Far East countries. Among in-hospital-treated patients
with peripheral artery occlusive disease, the prevalence rate is 45%–63% in India and 16%–66%
in Korea. The disease typically affects patients <45 years of age and is much more common in
men. TAO is a vasculitis characterized by a highly cellular thrombus with relative splitting of
the vessel wall. Patients with TAO have increased cellular immunity to types I and III collagen
compared with those who have arteriosclerosis. The prothrombin gene mutation 20210 and the
presence of anticardiolipin antibodies are associated with increased risk of disease. Hematocrit,
red blood cell rigidity, and blood viscosity are increased in patients with TAO as compared
to those with atherosclerosis. Nearly two-thirds of patients with TAO have severe periodontal disease and chronic anerobic periodontal infection. Polymerase chain reaction analysis
demonstrated DNA fragments from anerobic bacteria in both arterial lesions and oral cavities of
patients with TAO. TAO involves three phases: Acute, subacute, and chronic. In the acute phase,
there is a highly cellular occlusive inflammatory thrombus with polymorphonuclear neutrophils (PMNs), microabscesses, and multinucleated giant cells. The chronic phase is characterized by organized thrombus and vascular fibrosis that may mimic atherosclerotic disease.
However, in TAO there is preservation of the internal elastic lamina.
Correct Answer B Buerger disease (thromboangiitis obliterans)
Reference
Piazza, G., & Creager, M. A. (2010). Thromboangiitis obliterans. Circulation, 121(16), 1858–1861. PMID:
20421527
17. RATIONALE
Patients with TAO have involvement of distal small arteries and veins in both upper and lower
extremities. Although symptoms may begin in the peripheral portion of a single limb, the
disease frequently progresses proximally and involves multiple extremities. The initial presentation is that of symptoms of intermittent claudication of feet, legs, and hands. As the disease
advances, rest pain, ulceration, and digital gangrene occur. Raynaud phenomenon is present in
approximately 40% of patients with TAO and may be asymmetrical. Although most common in
the extremities, the disease may involve the cerebral, coronary, renal, mesenteric, and pulmonary arteries. Superficial thrombophlebitis differentiates TAO from other vasculitides and
atherosclerosis, although it may be observed in Behcet disease. Patients may describe a migratory pattern of tender nodules that follow the course of superficial veins. Neurological examination may document peripheral nerve involvement with sensory findings in up to 70% of patients.
Section 20: Rare Vascular Entities 353
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Correct Answer D Occlusion of distal small arteries and veins of lower and upper extremities
Reference
Piazza, G., & Creager, M. A. (2010). Thromboangiitis obliterans. Circulation, 121(16), 1858–1861. PMID:
20421527
18. RATIONALE
TAO is a clinical diagnosis made by pertinent history and physical findings and diagnostic vascular abnormalities on imaging studies. Clinical criteria include age <45 years, current or recent
history of tobacco use, exclusion of thrombophilia, autoimmune disease, diabetes mellitus, and
a proximal source of emboli. Lab testing in patients suspected of TAO is used to exclude alternative diagnoses. Serological markers of autoimmune disease are negative in TAO. Catheter based
arteriography provides the spatial resolution necessary to detect small artery pathology. Distal
small-to-medium artery involvement, segmental occlusions, and “corkscrew-shaped collaterals” around the area of occlusions are diagnostic of TAO without involvement of the proximal
limb arteries. Biopsy is rarely indicated and may result in non-healing of the incision.
Correct Answer D Distal small- to medium-sized arteries involvement, segmental occlusions, and corkscrew-shaped collaterals
Reference
Piazza, G., & Creager, M. A. (2010). Thromboangiitis obliterans. Circulation, 121(16), 1858–1861. PMID:
20421527
19. RATIONALE
The prognosis of patients depends largely on the ability to discontinue tobacco use. From the
French Buerger Network, the study revealed that 34% of patients with thromboangiitis obliterans will experience an amputation within 15 years from the diagnosis. Surgical reconstruction
is usually not feasible in patients with thromboangiitis obliterans because of the distant and
diffuse nature of the disease. Arterial bypass may be considered in a few select patients with
severe ischemia and suitable distal target vessels. Results of bypass surgery have suboptimal
outcomes, with primary patency rates of 41%, 32%, and 30% and secondary patency rates of 54%,
47%, and 39% at 1, 5, and 10 years, respectively, and the patency rates are 50% lower in patients
who continue to smoke after arterial bypass. Prostanoid vasodilator iloprost aids in the relief of
ischemic rest pain, greater healing of ischemic ulcers, and a two-thirds reduction in the need for
amputation. There is a limited role for intermittent pneumatic compression, spinal cord stimulation, and periarterial sympathectomy. Therapeutic angiogenesis has been attempted, but the
results require further investigation and confirmation. From a nationwide multicenter study of
224 patients with TAO with a mean follow-up of 5.7 years, vascular events were noted in 58.9%,
amputation in 21.4%, and death in 1.4%. A factor associated with amputation was limb infection.
Patients who stopped their tobacco consumption had a lower risk of amputation.
Correct Answer D 32%
Reference
Le Joncour, A., Soudet, S., Dupont, A., et al. (2018). Long-term outcome and prognostic factors of com-
plications in thromboangiitis obliterans (Buerger’s disease): a multicenter study of 224 patients.
J Am Heart Assoc, 7(23), e010677. PMID: 30571594
354 Section 20: Rare Vascular Entities
20. RATIONALE
The most important changes in the vasculature of patients with systemic sclerosis is Raynaud
phenomenon: A widespread form of vasospasm that is prodromal or concurrent with other
changes in systemic sclerosis. Systemic sclerosis is characterized by three distinct pathological
processes: Fibrosis, cellular/humoral, autoimmunity, and specific vascular changes. Although
a mild vasculitis may sometimes be present, the vascular pathology of systemic sclerosis is
best characterized as a vasculopathy. The injured cell type responsible for this vasculopathy
is endothelium. The major evidence of this is serological. Systemic sclerosis is characterized
by increased serum levels of von Willebrand factor, endothelium, and increased numbers of
circulating viable and dead endothelial cells. A common feature of systemic sclerosis is capillary malformation; intimal hyperplasia and capillary rarefaction are responsible for Raynaud
phenomenon. There is an inappropriate and exaggerated contraction of the small vessels in the
fingers and toes in response to cold or emotional distress that is present in 80%–90% of cases of
systemic sclerosis. Raynaud’s phenomenon can be the presenting symptom in approximately
33% of patients. The frequency and severity of Raynaud’s phenomenon in patients with systemic
sclerosis are often worse than that observed in patients with primary Raynaud’s phenomenon.
The incidence of ulcerations and gangrene is increased, leading to amputation in some patients.
Correct Answer D Raynaud’s phenomenon
Reference
Fleming, J. N., & Schwartz, S. M. (2008). The pathology of scleroderma vascular disease. Rheum Dis
Clin North Am, 34(1), 41–55; vi. PMID: 18329531
21. RATIONALE
Frostbite classification is based on the severity and extent of tissue damage after thawing, with
first-degree frostbite involving white patches of skin with edema and hyperemia, second-degree
involving blisters, third-degree involving full skin necrosis with subcutaneous extension, and
fourth-degree involving damage to muscle and bone and gangrene. Palpation can assist in differentiating superficial from deep frostbite. The affected area is stony hard or petrified when
deeper layers are affected. The best treatment for frostbitten fingers/hands is rewarming in a
warm (98–102°F) water bath. This is done until the affected part has become red and soft, and it
takes about 15–30 minutes. During rewarming, there is actually more cellular injury. This is due
to intimal damage in the small blood vessels. These changes are called reperfusion injury. Pain
during rewarming may require narcotics. Aspirin, clopidogrel, and calcium blockers may be
helpful. Additional treatment includes whirlpool baths, elevation of the effected part, and antiinflammatory medications. After frostbite, the fingers may become stiff, and physiotherapy may be
necessary. Prevention is the best treatment. Many patients suffer from long-term sequelae such as
vasomotor disturbances, neuropathic nociceptive pain, and damage to skeletal structures.
Correct Answer B Second degree
Reference
(2020). Frostbite in hands. Retrieved from https://ww w.assh.org/handcare/condition/frostbite-in-hands.
22. RATIONALE
Behcet’s disease is a chronic relapsing immunological syndrome. It occurs in the third or fourth
decade of life and is prevalent in Mediterranean countries, the Middle East, and East Asia.
Section 20: Rare Vascular Entities 355
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The disease is characterized by a classic triad of urogenital ulcerations, uveitis, retinal vasculitis, and erythema nodosum. The prognosis is determined by involvement of the cardiovascular, gastrointestinal, and central nervous system. Vascular complications occur in 7%–29% of
patients and have a major effect on mortality. Vascular lesions are most common in the venous
system; however, the arterial lesions are at greater risk. Involvement of a major artery is seen in
1.5%–2.2% of patients, often in the form of a rapidly expanding aneurysm. Pseudoaneurysm for-
mation at the anastomosis or at the site of angiographic puncture is also possible. Histological
examination of arterial lesions reveals leukocytoclastic arteritis, possibly responsible for ulceration and perforation of the arterial wall, and could explain the increased incidence of rupture
despite their small size compared with atherosclerotic aneurysm. The suture line is reinforced
with Teflon pledgets, and the intrabdominal prosthetic graft is wrapped with omentum.
Recurrent deep vein thrombosis and superficial thrombophlebitis are common manifestations.
Correct Answer B 7%–29%
Reference
Iscan, Z. H., Vural, K. M., & Bayazit, M. (2005). Compelling nature of arterial manifestations in Behcet
disease. J Vasc Surg, 41(1), 53–58. PMID: 15696044
23. RATIONALE
Paroxysmal finger hematoma (Achenbach syndrome) usually presents as recurring episodes of
an unexplained sudden onset of painful swelling associated with deep ecchymosis of the volar
aspect of the finger. The exact etiology remains unclear but is thought to be a vasomotor disorder. Owing to the self-limiting nature of this disease, invasive studies are not necessary and
would be negative if performed. The condition is self-limiting, and skin discoloration resolves
within an average of 4 days. The differential diagnosis is embolic digital artery occlusion from
thoracic outlet syndrome and dermatitis artefacta, which presents as a superficial erosion in
the hands of patients with chronic dermatitis. The diagnostic workup of a patient with purplish
discoloration of a finger, with or without a diminished radial pulse, should include a Doppler
arterial study and duplex ultrasound scan of the left subclavian artery to exclude a subclavian
artery aneurysm in association with thoracic outlet syndrome. Raynaud’s disease typically
presents as episodes of a patient’s fingers (unusually all) turning pale, followed by purplish
discoloration. It is accompanied by paresthesias and cold sensation in both hands. The fingers
will then turn warm and red as the vasospasm subsides. In contrast to Raynaud’s phenomenon,
systemic sclerosis in most instances is unilateral.
Correct Answer C Achenbach syndrome (paroxysmal finger hematoma)
Reference
Lehman, H., Acho, R., & Hans, S. S. (2021). Achenbach syndrome as a rare cause of painful, blue finger.
J Vasc Surg Cases Innov Tech, 7(3), 589–592. PMID: 34541431
24. RATIONALE
Fibromuscular dysplasia is classified according to the affected segment of the arterial wall.
The same classification is used for all the arteries affected by fibromuscular dysplasia. Medial
fibroplasia is the most common (80%–90%) with a “string-of-beads” appearance secondary to
alternating thinned and thickened medial ridges. This appearance on arteriography is
secondary to stenotic webs that cause sequential stenosis and dilatations in the arterial wall.
356 Section 20: Rare Vascular Entities
These dilatations may lead to aneurysmal degeneration. Intimal fibroplasia is responsible for
about 10% of cases of fibromuscular dysplasia, resulting in a long concentric stenotic lesion
secondary to intimal collagen deposits. The differential diagnosis is atherosclerosis, vasculitis,
and connective tissue disorder.
Correct Answer B Medial fibroplasia
Reference
Poloskey, S. L., Olin, J. W., & Mace, P. (2012). Fibromuscular dysplasia. Circulation, 125(18), e636–e639.
PMID: 22566353
25. RATIONALE
Most patients with cerebrovascular FMD are asymptomatic middle-aged women who are otherwise healthy. The cause of FMD is unknown. Approximately 10% of patients with FMD have an
affected family member as well. Patients may present with headaches or dizziness, and a carotid
bruit may be detectable on physical examination. The incidence of ischemic cerebral events is
quite low at long-term follow-up. Occasionally cerebral ischemia is secondary to a thromboemboli originating from a diseased arterial segment or from a low-flow state. Patients may present with arterial dissection. There is a higher incidence of intracranial aneurysms in patients
with internal carotid artery or vertebral artery fibromuscular dysplasia. Duplex ultrasound is a
standard first-line modality in diagnosing fibromuscular dysplasia. However, Doppler velocity
diagnostic criteria applicable to atherosclerotic disease are not reliable in diagnoses of fibromuscular dysplasia. CTA and MRA of the neck are useful techniques in diagnosing fibromuscular dysplasia. CTA is preferable, but MRA may be helpful in diagnosing concurrent arterial
dissection through simultaneously acquired T1-fat saturation images with time-of-flight or
gadolinium-enhanced imaging. Low-dose aspirin is indicated. Duplex surveillance to rule out
aneurysmal degeneration should be obtained on a yearly basis. In selected cases balloon angioplasty is indicated in patients who fail medical management and the lesion is progressive.
Correct Answer A Result of atherosclerosis
Reference
Kadian-Dodov, D., Gornik, H. L., Gu, X., et al. (2016). Dissection and aneurysm in patients with fibro-
muscular dysplasia: findings from the U.S. registry for FMD. J Am Coll Cardiol, 68(2), 176–185.
PMID: 27386771
SECTION 21: BIOSTATISTICS
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MCQs 1–11
Q1. Which of the following would be most likely
to produce a selection bias in a sample:
A. Only receiving a response from 60% of
the people in the sample
B. Biased wording in the questionnaire
C. Interviews conducted on the phone in
place of in-person interview
D. Recruiting participants directly from clinics,
who miss all the care who do not attend the
clinic, or who seek care during the study
Q2. Which one of these statistic measures is
unaffected by outliers:
A. Mean
B. Standard deviation
C. Range
D. Interquartile range
Q3. The regression line determines if:
A. Any X values are outliers
B. Any Y values are outliers
C. To estimate the changes in Y for a unit
change in X, this assumes that the relationship between X and Y is linear
D. To determine if a change in X causes a
change in Y, this assumes that the relationship between X and Y is linear
Q4. A Chi-square test of the relationship
between the perception of emotional
health and marital status leads to a rejection of the null hypothesis, indicating
that there is a relationship between the
two variables. The conclusion that can be
drawn is:
A. Better emotional health results in better
marriage
B. If one is more emotionally healthy, the
more likely they are to be married
C. There are likely to be confounding vari-
ables related to marital status as well as
emotional health
D. Marriage leads to better emotional health
Q5. Propensity score matching (PSM) is a
statistical matching technique that:
A. Is used in the analysis of contingency
tables (Fisher exact) when sample sizes
are small
B. Statistical hypothesis used in the analysis
of contingency tables when the sample
sizes are large (Chi-square analysis)
C. Step function illustrating the survival
probability over time (Kaplan–Meier
survival curve)
D. Estimates the effect of the treatment
policy by accounting for the covariates
that predict receiving the treatment
Q6. If a p-value of a test statistic results esti-
mates at 0.0596, what is the probability of
falsely rejecting H
A. 5.96%
B. 5.09%
C. 5.91%
D. 5.06%
(null hypothesis)?
0
DOI: 10.1201/9781003389897-21
358 Section 21: Biostatistics
Q7. Type II error means:
A. Rejecting the null hypothesis when it is
false
B. Rejecting the null hypothesis when it is
true
C. Not rejecting the null hypothesis when it
is actually false
D. Not rejecting the null hypothesis when it
is true
Q8. If 17 smokers have lung cancer, 83 smok-
ers do not have lung cancer, 1 non-smoker
has lung cancer, and 99 non-smokers do
not have lung cancer, the odds ratio (this
hypothetical group of smokers) is:
A. 10 times the odds of having lung cancer
B. 15 times the odds of having lung cancer
C. 20 times the odds of having lung cancer
D. 25 times the odds of having lung cancer
Q9. A new noninvasive vascular test is to diag-
nose middle cerebral artery stenosis. All
patients had a cerebral arteriogram, considered the “gold standard,” as well as the
new noninvasive vascular test. Out of 100
patients the cerebral angiogram reported
78 studies were positive and
22 studies were negative. Out of 78 patients
reported by angiogram, 72 were reported
positive by the new test and 6 were
reported as negative. Out of the 22 patients
reported as negative by the angiogram,
16 were reported as negative by the new
test and 6 were reported as positive. The
positive predictive value (PPV) and the
negative predictive value (NPV) of the new
test are:
A. PPV 92.3NPV 70.7
B. PPV 90.3NPV 70.7
C. PPV 92.3NPV 72.7
D. PPV 95.3NPV 74.7
Q10. In the aforementioned sample test
(question 9), the sensitivity and specificity
are:
A. Sensitivity 81.8%Specificity 72.7%
B. Sensitivity 92.3%Specificity 70.7%
C. Sensitivity 92.3%Specificity 72.7%
D. Sensitivity 91.8%Specificity 72.7%
Q11. The accuracy of the test in question 9 is:
A. 88%
B. 92%
C. 96%
D. 98%
Section 21: Biostatistics 359
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RATIONALE 1–11
1. RATIONALE
Selection bias is a distortion in a measure of association (such as a risk ratio) due to a sample
selection that does not accurately affect the targeted population. Selection bias can occur when
investigators use improper procedures for selecting a sample population, but it can also occur
because of factors that influence the continued participation of subjects in a study. In either
case, the final study population is not representative of the targeted population. Selection bias
occurs when the association between the exposure and health outcome is different for those
who complete a study compared with those who are in the target population. Causes of selection biases are selective survival and losses to follow-up, volunteer and non-response bias, and
hospital patient bias. Selection bias often occurs in observational studies where the selection is
not random and is called undercoverage bias.
Correct Answer D Recruiting participants directly from clinics, who miss all the care who do
not attend the clinic, or who seek care during the study
Reference
Rothman, K. J., Greenland, S., & Lash, T. L. (2008). Validity in epidemiologic studies. In K. J. Rothman,
S. Greenland, & T. L. Lash (Eds.), Modern epidemiology (3rd ed.). Philadelphia, PA: Lippincott
Williams & Wilkins.
2. RATIONALE
Interquartile range (IQR) is a measure of statistical disposition, which is the spread of the data.
The IQR may also be referred to as mid-spread/middle 50%, fourth spread, or H-spread and is
defined as the difference between the 75th and 25th percentiles of the data. To calculate IQR the
data set is divided into quartiles of four evenly ranked parts. These quartiles are denoted by Q1
(lower quartile), Q2 (the median quartile), and Q3 (upper quartile). The lower quartile corresponds with the 25th percentile and upper quartile with the upper 75th percentile.
Correct Answer D Interquartile range
Reference
Dekk ing, F. M., Kraaikamp, C., Lopuhaä, H. P., et al. (2005). Testing hypotheses: elaboration. In A mod-
ern introduction to probability and statistics: understanding why and how (pp. 383–397). London:
Springer London.
3. RATIONALE
A regression line indicates a linear relationship between the dependent variable in the Y axis
and the independent variable in the X axis. The correlation is established by analyzing the data
formed by the variable. The regression line is plotted closest to the data point in a regression
graph. The formula for simple linear regression is Y = mX + b, where Y is the response (dependent) variable, m is the estimated slope, and b is the estimated intercept. You can calculate the
regression line for two variables if their scatter plot shows a linear pattern and the correlation
between the variables is very strong (r = 0.98). A regression line is simply a single line that best
fits the data (smallest overall distance from the line to the points). Finding the best-fitting line is
referred to as a simple linear regression analysis using the least squares method. The mean of
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