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MCCQE1 > Epidemiology and biostats > Flashcards

Epidemiology and biostats Flashcards

1
Q

In what kind of study is Relative risk is used?

A

Cohort

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2
Q

In what kind of study is odds ratio is used?

A

Case-control

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3
Q

Interpretation of RR and OR?

A

> 1: positive association
= 1: no association
< 1: negative association (protective)

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4
Q

What is sensitivity

A

Given that I have the disease how likely is that I’ll have a positive test

True positive / Disease (+) = True positive / (True positive + False negative)

Sensible tests are used as screening tests

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5
Q

What is specificity

A

Given that I am disease-free how likely is that I’ll have a negative test

True negative / Disease (-) = True negative / (False positive + True negative)

Specific tests are used as a confirmatory test after a positive screening

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6
Q

What is positive predictive value

A

Given that I have a positive test how likely is that I have the disease

True positive / Positive test = True positive / (True positive + False positive)

The higher the prevalence, the higher the PPV will be

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7
Q

What is negative predictive value

A

Given that I have a negative test how likely is that I don’t have the disease

True negative / Negative test = True negative / (True negative + False negative)

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8
Q

Accuracy vs precision

A

Precision measures the consistency of the results (if I repeat the test, how likely is that I will have the same results)

Accuracy measures that the test measure what it is intended to measure

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9
Q

Bias from participants and how to address them

A
  • Hawthorne effect: People change their behaviour because they know they’re being observed
  • Recall bias: sick patients remember more

Addressed by blinding

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10
Q

Bias from researcher and how to address them

A

Selection bias: at baseline, the groups are different in way they shouldn’t be
• Addressed by randomization and matching

Observer bias: The researcher knows who is in control and intervention groups
• Addressed by blinding

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11
Q

You find in a study that ice-cream consumption is associated with drowning.

What type of bias is this?

A

Confounding:
Relationship between exposure and outcome is distorted because a third factor is related to both exposure and outcome.

In this case the third factor is summer

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12
Q

OCP have a small association with DVT. However, when smoking, the association between OCP and DVT is highly enhanced.

Type of bias?

A

Effect modification:

The relationship between exposure and outcome is enhanced by a third factor, which only affects the outcome and not the exposure

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13
Q

Case-control study or cohort study. Which one is better for a rare disease?

A

Case-control study

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14
Q

What is the type I error?

A

Saying there’s a difference when in reality there is none

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15
Q

What is the type II error?

A

Saying there’s no difference when in reality there is

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16
Q

What is primary prevention?

A

o They don’t have yet the disease
o Goal: Keep the patient healthy
o Reduce exposure to risk factors
o Examples: weight loss, smoking cessation, reduce EtOH, healthy eating. vaccination

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17
Q

What is secondary prevention?

A

o They already have the disease

o Goal: delay progression by detecting the disease in an early stage (screening) and start early treatment if needed

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18
Q

What is tertiary prevention?

A

o Goal: prevent complications from an existing disease with acting therapy

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19
Q

Colon cancer screening guidelines

A

Start: 50 yrs or 10 yrs before the Dx of a primary relative

How: Flex sigmoidoscopy / 10 yrs Or Fecal occult blood test / 2 yrs

Stop: 75 yrs

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20
Q

Breast cancer screening guidelines

A

Start: 50 yrs

How: Mamography / 2 yrs

Stop: 75 yrs

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21
Q

Cervical cancer screening guidelines

A

Start: 21 yrs

How: Pap smear / 3 yrs

Stop: 70 yrs if 3 consecutive negative pap smears

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22
Q

Lungcancer screening guidelines

A

Start: 55–75 with history of > 30 pack-year who quit < 15 yrs ago

How: Low dose CT scan / yrs

Stop: 80 yrs or quit > 15 yrs ago

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23
Q

Cancers you don’t screen for

A

Prostate and ovarian

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24
Q

Abdominal aortic aneurism. Who and how to screen?

A

Men > 65 and Women > 65 who have ever smoked

Abdominal U/S

25
Q

Osteoporosis. Who and how to screen?

A

Women > 65

DEXA scan (if positive, bisphosphonates)

26
Q

Hep C. Who and how to screen?

A

Baby boomer (1945–1965)

Hep C Ab

27
Q

HIV. Who and how to screen?

A

Everyone

ELISA

28
Q

HTN, Who and how to screen?

A

Everyone

Ambulatory monitoring

29
Q

DM. Who and how to screen?

A

> 40 or at high risk / 3 yrs

A1C

30
Q

Dyslipidemia. Who and how to screen?

A

♀ 45 yrs; 30 if high risk
♂ 35 yrs ; 25 if high risk

Lipid panel

31
Q

Bias introduced into a study when a clinician is aware of the patient’s treatment type.

A

Observational bias.

32
Q

Bias introduced when screening detects a disease earlier and thus lengthens the time from diagnosis to death.

A

Lead-time bias.

33
Q

If you want to know if geographical location affects infant mortality rate but most variation in infant mortality is predicted by socioeconomic status, then socioeconomic status is a _____.

A

Confounding variable.

34
Q

The number of true positives divided by the number of patients with the disease is _____.

A

Sensitivity.

35
Q

Sensitive tests have few false negatives and are used to rule _____ a disease.

A

Out.

36
Q

PPD reactivity is used as a screening test because most people with TB (except those who are anergic) will have a (+) PPD. Highly sensitive or specific?

A

Highly sensitive for TB.

37
Q

Chronic diseases such as SLE—higher prevalence or

incidence?

A

Higher prevalence.

38
Q

Epidemics such as influenza—higher prevalence or

incidence?

A

Higher incidence.

39
Q

Cross-sectional survey—incidence or prevalence?

A

Prevalence.

40
Q

Cohort study—incidence or prevalence?

A

Incidence and prevalence.

41
Q

Case-control study—incidence or prevalence?

A

Neither.

42
Q

Describe a test that consistently gives identical results, but the results are wrong.

A

High reliability, low validity.

43
Q

Difference between a cohort and a case-control study.

A

Cohort studies can be used to calculate relative risk (RR), incidence, and/or odds ratio (OR). Case-control studies can be used to calculate an OR.

44
Q

Attributable risk?

A

The incidence rate (IR) of a disease in exposed – the IR of a disease in unexposed.

45
Q

Relative risk?

A

The IR of a disease in a population exposed to a particular factor ÷ the IR of those not exposed.

46
Q

Odds ratio?

A

The likelihood of a disease among individuals exposed to a risk factor compared to those who have not been exposed.

47
Q

Number needed to treat?

A

1 ÷ (rate in untreated group – rate in treated group).

48
Q

In which patients do you initiate colorectal cancer screening early?

A

Patients with IBD; those with familial adenomatous polyposis (FAP)/hereditary nonpolyposis colorectal cancer (HNPCC); and those who have first-degree relatives with adenomatous polyps (< 60 years of age) or colorectal cancer.

49
Q

The most common cancer in men and the most common cause of death from cancer in men.

A

Prostate cancer is the most common cancer in men, but lung cancer causes more deaths.

50
Q

The percentage of cases within one SD of the mean? Two SDs? Three SDs?

A

68%, 95.4%, 99.7%.

51
Q

Birth rate?

A

Number of live births per 1000 population in one year.

52
Q

Fertility rate?

A

Number of live births per 1000 females (15–44 years of

age) in one year.

53
Q

Mortality rate?

A

Number of deaths per 1000 population in one year.

54
Q

Neonatal mortality rate?

A

Number of deaths from birth to 28 days per 1000 live births in one year.

55
Q

Postnatal mortality rate?

A

Number of deaths from 28 days to one year per 1000 live births in one year.

56
Q

Infant mortality rate?

A

Number of deaths from birth to one year of age per 1000 live births (neonatal + postnatal mortality) in one year.

57
Q

Fetal mortality rate?

A

Number of deaths from 20 weeks’ gestation to birth per 1000 total births in one year.

58
Q

Perinatal mortality rate?

A

Number of deaths from 20 weeks’ gestation to one month of life per 1000 total births in one year.

59
Q

Maternal mortality rate?

A

Number of deaths during pregnancy to 90 days postpartum per 100,000 live births in one year.

MCCQE1 (19 decks)

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