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USMLE Step 1 > Biostatitics - Review > Flashcards

Biostatitics - Review Flashcards

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USMLE® Step 1 flashcards
1
Q

Recall bias

A

results from inaccurate recall of past exposure

  • applies mostly to retrospective control studies
  • people who have suffered adverse effects are more likely to recall risk factors than those who don’t
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2
Q

Referral bias

A
  • ocurs when the case and control populations differ due to admission or referral pracrices
  • example, study involving cancer risk performed at cancer research hospital may enroll cases referred all over the nation however, hospitalized control
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3
Q

Detection bias

A

refers to risk factor itself may itself may lead to intensive investigation and may increase probability of finding disease

  • patients who smoke may undergo increased imaging due to smoking status
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4
Q

Lead time bias

A

occurs when screening test diagnoses a disease earlier than it would have appeared by natural history so time from diagnosis until death appears longer
- affected studies may not accurately reflect improvement in health

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5
Q

Allocation bias

A

results from how the treatment and control are assembled. May occur if subjects are assigned to study groups of clinical trial in a non-random fashion

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6
Q

Hawthorne effect

A

tendency of study population to affect outcome due to knowledge of being studies

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7
Q

Berkson’s bias

A

selecting hospitalized patients as control group

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8
Q

Pygmalion effect

A

describes researcher’s effect in the efficacy of treatment that can potentially affect outcome

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9
Q

Cystinuria

A

caused by defect in renal proximal tubules which result in decreased resorption of amino acid cysteine

  • renal stones at young age
  • hexagonal cystine crystals
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10
Q

Sodium cyanide nitroprusside tests

A

detects cystine’s sulfhydryl groups

- turns purple

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11
Q

Primary oocytes

A
  • developed by 5th month of gestation

- arrested in PROPHASE of meiosis I

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12
Q

Secondary oocytes

A
  • arrested in METAPHASE of meosis II prior to fertilization
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13
Q

Sx: Simultaneous development of stroke, foot/intestinal ischemia and renal infarction. Likely diagnosis

A

Embolic phenomena

- often caused by left atrial clots, left ventricular clots, valvular vegetations, and aortic sclerotic plaques

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14
Q

Sx: Signs of renal failure (increased creatinine) and toe gangrene/livedo reticularis. Likely diagnosis?

A

Atheroembolic renal disease

- cholesterol emboli obstructs renal arterioles

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15
Q

Sx: Urinary hestinancy, urgency, frequency, incomplete coiding, post-void leakage in men > 60 years old.

A

BPH

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16
Q

Prostate

A

found between pubic symphysis and anal canal

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17
Q

Common causes of impetigo

A

S. aureus and Group A Strep

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18
Q

Post-streptococcal glomerulonephritis

A
  • follows pharyngitis or skin infection (impetigo)
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19
Q

Conditions caused by incomplete obliteration of processus vaginalis

A

Hydrocele

Indirect inguinal canal

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20
Q

Hydrocele

A
  • due to incomplete obliteration of processus vaginalis

- occurs when there is connection between scrotum and abdominal cavity that allows for leakage of fluid

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21
Q

Secretory phase of menstrual cycle

A
  • occurs between ovulation and menses
  • progesterone released by corpus luteum causes uterine glands to coil and secrete mucus-rich secretions and plumps up endometrium
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22
Q

In follicular phase, what hormone mediates endometrial proliferation?

A

Estrogen

  • glands appear straight and narrow (small lumens)
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23
Q

In secretory phase, what hormone mediates endometrial proliferation

A

Progesterone

- glands appear dilated and coiled (wide lumens)

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24
Q

Best way to visualize T. pallidum

A

Darkfield microscopy

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25
Q

Cryptochordism

A
  • undescended testes
  • normal testosterone levels but low sperm (in adults)
  • if uncorrected, seminiferous tubules atrophy and Sertoli cells secrete less inhibin
  • increased risk of testicular cancer
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26
Q

Sertoli cells

A
  • found in seminiferous tubules
  • secrete INHIBIN - which inhibits FSH
  • support sperm synthesis
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27
Q

Leydig cells

A
  • secrete testosterone
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28
Q

Annovulation

A
  • common in first five to seven years after menarche and last years before menophause
  • manifests with marked menstrual in variability
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29
Q

FSH levels in menopause

A

Elevated FSH levels in menopause

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30
Q

Phenylepherine

A

alpha agonist with some selectivity for alpha 1 receptors

- would encourage urinary retention

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31
Q

Treatment for urinary retention

A 
Muscarinic agent (bethanecol)
or alpha-blocking agents
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32
Q

Finasteride

A
  • prescribed to patients urinary retention secondary to BPH

- 5-alpha reductase inhibitor which decreases DHT, which would decrease hypertrophy of bladder

33
Q

Hydronephrosis

A

dilation of renal pelvis and calyces due to obstruction of urine flow

  • kidney enlargement and distortion, compression of papillae, and thinning of parenchyma around calyces seen
  • commonly caused by BPH
34
Q

Treatment for patients presenting with calcium stones with hyperoxaluria

A

low sodium diets

35
Q

Ectopic pregnancy

A
  • higher occurence in patients with PID
  • abdominal pain, vaginal bleeding, hemorrhagic shock, and amenorrhea
  • biopsy shows decidual changes but no chorionic villi
36
Q

Sildenafil

A

inhibitor of cGMP phosphodierase

- NO and ANP use this mechanism

37
Q

Signs of urethral injury

A
  • inability to void despite sensation of full bladder
  • high riding boggy prostate
  • blood in urethral meatus
38
Q

Injury to posterior urethra

A

associated with pelvic fracture

39
Q

Injury to anterior urethra

A

associate with straddle injuries

40
Q

Hormones that prevent lactation during pregnancy

A

Estrogen and progesterone

41
Q

B-lactamase inhibitors

A

Clavulanic acid
Sulbactam
Tazobactam

** extend the spectrum of penicilin binding antibiotics by decreasing their destruction

42
Q

Tazobactam-Piperacillin

A
  • Tazobactam - B-lactamase inhibitor allows piperacillin to act on gram negative bacteria that would not be vulnerable to piperacillin alone
43
Q

BPH

A
  • epithelial and stromal hyperplasia, mostly in periurethral and transitional zones
  • urinary retention as a result leads to increased pressure in urinary tract, nephropathy, and hydronephrosis
44
Q

Organs that drain to superficial inguinal lymph nodes

A
  • all skin from umbilicus down (up to pectinate line) drains to superficial inguinal lymph nodes
45
Q

Testicular hydrocele

A
  • when serous fluid accumulates in tunica vaginalis

- results when processus vaginalis fails to close

46
Q

Contraindications to OCPs

A
  • Prior embolic event (stroke, PE, MI)
  • History of estrogen dependent tumor
  • Women over 35 who smoke
  • Hypertriglyceridemia
  • Liver disease
  • Pregnancy
47
Q

Gram-negative sepsis is caused by which bacterial factor?

A

LPS

  • it is NOT secreted by bacteria but part of outer membrane
  • induces activation of macrophages leading to IL-1 and TNF-alpa
48
Q

Signs of septic shock

A 
Fever
hypotension
Diarrhea
Oliguria
Vascular compromise
DIC
49
Q

TNF-alpha

A

cytokines that induces systemic inflammatory response

- causes septic shock

50
Q

Cytokines responsible for inducing systemic inflammatory response

A

IL-1
IL-6
TNF-alpha

51
Q

Which mechanism does mifepristone use to terminate early pregnancy

A

Anti-progestin

52
Q

Endometrial cells undergo what process upon withdrawal of progesterone

A

Apoptosis

53
Q

Calcium oxalate/ calcium phosphate

A
  • radiopaque
  • octahedron
  • most common
54
Q

Magnesium struvite

A
  • radiopaque

- resemble coffin lids (retangular prism)

55
Q

Uric acid

A
  • RADIOLUCENT

- yellow/red-brown diamond/rhombus

56
Q

Cysteine

A
  • Radiopaque
  • hexagonal
  • least common
57
Q

Vasectomy

A
  • transection of vas deferens
  • has no effect on sperm proximal to ligation
  • patients may still have viable sperm 3 months and at least 20 ejaculations
58
Q

Pathogenesis of acute pyelonephritis

A
  • vesicoureteral reflux
59
Q

Pathogenesis of lower UTIs

A
  • suppression of indigenous flora
  • colonization of distal urethra by gram - rods
  • attachment of gram - pathodesnt to bladder mucosa
60
Q

Sx: Adnexal mass in elderly female

A
  • Likely ovarian malignancy
61
Q

Serum marker for recurrence of ovarian malignancy

A

CA-125

62
Q

Sx: fever, maculopapular rash and symptoms of ARF, 1-3 week after beginning treatment with B-lactam antibiotic

A

suggests interstitial neprhitis

  • peripheral eosinophilia and eosinophiluria
  • symptoms will stop after cessation of medication
63
Q

Serum and urine levels associated with calcium kidney stone

A
  • Normocalcemia

- Hypercalciuriae

64
Q

Standard treatment for N. gonorrthoae

A
  • Ceftriaxone ( for the N. gonorrohoe) + Doxycycline or Azithromycin for possible co-infection of C. trachimatis
65
Q

Mechanism of OCPs

A
  • doses of estrogen and progesterone

decrease synthesis of FSH and LH in anterior pituitary thus decreasing gonadotropin levels

66
Q

Type I error

A

when researchers reject a TRUE null hypothesis

b/b+d (kind of like specificity)

Alpha - probability of making a type 1 error, typtically set at p = 0.05

67
Q

Type II

A

when researchers accept a FALSE null hypothesis

c/a+c - (kind of like sensitivity)

B - probability of commiting type 2 error

68
Q

Alpha (in terms of biostatistics)

A

maximum probability of committing a type I error

typically accepting p = 0.05

69
Q

Beta ( in terms of biostatistics)

A

maximum probability of committing a type II error (accepting a false null hypothesis)

70
Q

Power

A

(1 - Beta)

probability of rejecting a null hypothesis when it is truly false

71
Q

Observer Bias

A

to prevent patient or researcher expectancy from interfering with determining outcome
- often prevented by blinding patients OR both patients and physicians from the groups

72
Q

Selection bias

A

results from manner in which people are selected for the study, or from the selective losses from follow-up

73
Q

Odds Ratio

A

ad/bc

74
Q

Relative Risk

A

a/(a+b) - c/(c+d)

75
Q

Prospective cohort study

A

initially a group of subjects is selected and their exposure status is determined. The cohort is then followed for a certain amount of time and observed for development of outcome

76
Q

Retrospective cohort study

A

exposure status is determied retrospectively and then that person is tracked from that point of time, using medical records

77
Q

Cross sectional study

A

simultaneous measure of exposure and outcome

- uses surveys

78
Q

Case control

A

selecting patients with particular disease (cases) and with that disease (controls) and then determining exposure status

USMLE Step 1 (34 decks)

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