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USLME > FARR Epidemiology > Flashcards

FARR Epidemiology Flashcards

1
Q

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

A

Observational bias.

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2
Q

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

A

Lead-time bias.

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3
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.

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4
Q

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

A

Sensitivity.

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5
Q

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

A

Out.

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6
Q

PPD reactivity is used as a screening test because most people with TB (except those who are anergic) will have a

A

Highly sensitive for TB.

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7
Q

Cohort study—incidence or prevalence?

A

Incidence and prevalence.

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8
Q

Case-control study—incidence or prevalence?

A

Neither.

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9
Q

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

A

High reliability, low validity.

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10
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.

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11
Q

Attributable risk?

A

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

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12
Q

Relative risk?

A

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

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13
Q

Odds ratio?

A

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

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14
Q

Number needed to treat?

A

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

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15
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.

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16
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.

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17
Q

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

A

68%, 95.4%, 99.7%.

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18
Q

Birth rate?

A

Number of live births per 1000 population in one year.

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19
Q

Fertility rate?

A

Number of live births per 1000 females (15–44 years of age) in one year.

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20
Q

Mortality rate?

A

Number of deaths per 1000 population in one year.

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21
Q

Neonatal mortality rate?

A

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

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22
Q

Postnatal mortality rate?

A

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

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23
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.

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24
Q

Fetal mortality rate?

A

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

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25
Q

Perinatal mortality rate?

A

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

26
Q

Maternal mortality rate?

A

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

27
Q

False-neg ratio =

A

1 – sensitivity

28
Q

False-pos ratio =

A

1 – specificity

29
Q

Sensitivity =

A

a/(a+c)

30
Q

Specificity =

A

d/(b+d)

31
Q

PPV =

A

a/(a + b)

32
Q

NPV =

A

d/(c + d)

33
Q

High sensitivity is particularly desirable when

A

there is a significant
penalty for missing a disease. It is also desirable early in a diagnostic workup, when it is necessary to reduce a broad differential. Example: An initial ELISA test for HIV infection.

34
Q

High specificity is useful for confirming

A

a likely diagnosis or for situa- tions in which false-

35
Q

The positive predictive value (PPV) is

A

the probability that a patient with a

36
Q

The negative predictive value (NPV) is

A

he probability that a patient with a

37
Q

Advantages of cohort studies are as follows:

A

They follow the same logic as the clinical question (if people are ex-
posed, will they get the disease?).
I They are the only way to directly determine incidence.
I They can be used to assess the relationship of a given exposure to many
diseases.
I In prospective studies, exposure is elicited without bias from a known
outcome.

38
Q

The disadvantages of cohort studies include the following:

A

They can be time consuming and expensive.
I Studies assess only the relationship of the disease to the few exposure
factors recorded at the start of the study.
I They require many subjects and are thus inefficient and cannot be
used to study rare diseases.

39
Q

The validity of a case-control study depends on

A

appropriate selection of cases and controls, the manner in which exposure is measured, and the manner in which extraneous variables (confounders) are dealt with.

40
Q

Advantages of such studies are as follows:

A

I Studies use small groups, thereby reducing expense.
I They can be used to study rare diseases and can easily examine mul-
tiple risk factors.

41
Q

Disadvantages include the following:

A

Studies cannot calculate disease prevalence, incidence, or relative risk, because the numbers of subjects with and without a disease are deter- mined artificially by the investigator rather than by nature (an odds ra- tio can be used to estimate relative risk).
I Retrospective data may be inaccurate owing to recall or survivorship biases.

42
Q

Absolute risk:

A

Defined as the incidence of disease.

43
Q

Attributable risk (or risk difference):

A

The additional incidence of disease
that is due to a risky exposure, on top of the background incidence from other causes.
Attributable risk = Incidence of disease in exposed – Incidence in unexposed

44
Q

Relative risk (or risk ratio):

A

Expresses how much more likely an exposed person is to get disease in comparison to an unexposed person. This indi- cates the strength of the association between exposure and disease, mak- ing it useful when one is considering disease etiology.

Relative risk = Incidence in exposed Incidence / in unexposed

45
Q

Odds ratio:

A

An estimate of relative risk that is used in case-control studies. The odds ratio tells how much more likely it is that a person with a disease has been exposed to a risk factor than someone without the disease. Thelower the disease incidence, the more closely it approximates relative risk (see Figure 2.4-2).

46
Q

A randomized controlled trial is

A

an experimental, prospective study in which subjects are randomly assigned to a treatment or control group.

47
Q

Advantages of randomized controlled trials are as follows:

A

I They involve minimal bias.

I They have the potential to demonstrate causal relationships.

48
Q

Disadvantages include the following:

A

They are costly and time intensive.
I Informed consent may be difficult to obtain.
I Some interventions (e.g., surgery) are not amenable to masking. I Ethical standards cannot allow all variables to be controlled.

49
Q

Bias

Defined as

A

any process that causes results to systematically differ from the truth. Good studies and data analyses seek to minimize potential bias.

50
Q

Types of bias include the following:

A 
Selection bias:
Measurement bias:
Confounding bias:
Recall bias:
Lead-time bias:
Length bias:
51
Q

Type I (α) error:

A

Defined as the probability of saying that there is a difference in treat-
ment effects between groups when in fact there is not (i.e., a false-

52
Q

Type II (β) error:

A

Defined as the probability of saying that there is no difference in treat- ment effects (i.e., a false-

53
Q

If one is using a 95% CI, there is a

A

95% chance that the interval con-
tains the true effect size, which is likely to be closest to the point esti-
mate near the center of the interval.

54
Q

Live attenuated

A

Measles, mumps, rubella, polio (Sabin), yellow fever, influenza (nasal spray).

55
Q

Inactivated (killed)

A

Cholera, influenza, HAV, polio (Salk), rabies, influenza (injection).

56
Q

Toxoid

A

Diphtheria, tetanus.

57
Q

Subunit

A

HBV, pertussis, Streptococcus pneumoniae, HPV, meningococcus.

58
Q

Conjugate

A

Hib, S. pneumoniae.

59
Q

Prevention may be accomplished by

A

a combination of immunization, chemoprevention, behavioral counseling, and screening.

60
Q

A good screen- ing test has the following characteristics:

A

It has high sensitivity and specificity.
I It has a high PPV.
I It is inexpensive, easy to administer, and safe.
I Treatment after screening is more effective than subsequent treatment
without screening.

61
Q

Ottawa Charter

A 
Healthy public policy
supportive environment
strengthen community actions
develop personal skills
reorient health services

USLME (41 decks)

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