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Epidemiology > Module 7 > Flashcards

Module 7 Flashcards

1
Q

Cross-sectional study- how to best look at it

A

Snapshot of the population you wish to learn about
A small replica of all parts of the population: often proportional to size

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2
Q

Key features of cross-sectional studies

A

-A type of prevalence study
-Single period of observation. No f/u.
-Exposure and dz data collected simultaneously.
-Exposure and dz measures obtained at the individual level.
-Both probability and non-probability sampling used.
-Best done as a probability sample.

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3
Q

Characteristics of a cross-sectional survey

A

-Conducted over a short period of time
—For small studies- a few days or weeks
—For large studies with thousands of participants- a few years
-The unit of analysis is the individual
-There is no f/u period.

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4
Q

a in the cross-section table

A

Was exposed and has the dz

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5
Q

b in the cross-section table

A

Was exposed, did not get the dz

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6
Q

c in the cross-section table

A

Was not exposed, got the dz

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7
Q

d in the cross-section table

A

Was not exposed, did not get the dz

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8
Q

Familiar examples of cross-sectional studies

A

Opinion polls of all kinds:
-All political polls
-Telephone surveys
-Surveys done by companies about their products

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9
Q

Definition of serial surveys

A

Cross-sectional surveys that are routinely (repeatedly) conducted
Each serial survey recruits different people in each cycle

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10
Q

Examples of serial surveys

A

Behavioral Risk Factor Surveillance System
National Health Interview Survey
National Hospital Discharge Survey
National Health and Nutrition Examination Survey

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11
Q

Probability sample definition

A

Every element in the population has a quantifiable probability of being included in the sample

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12
Q

Types of probability samples

A

Simple random sample
Systematic random sample
Stratified probability sample

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13
Q

Non-probability sample definition

A

It is impossible to quantify the probability of being included in the sample

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14
Q

What is a type of sample that is a non-probability sample?

A

Convenience sample

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15
Q

Simple random sample characteristics

A

Everyone in the sources pop has an equal chance of getting into the study
Participants are chosen completely at random

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16
Q

Systematic random sample characteristics

A

Like a simple random sample, but the investigators choose every nth person to invite into the study, from a list, called the sample frame, representing the source population

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17
Q

Stratified probability sample characteristics

A

Identify subgroups in the pop, such as racial/ethnic groups
And take a random sample of each subgroup
Most large surveys, like NHANES are this type

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18
Q

Characteristics of convenience sample

A

Not a probability sample
Only interview whomever you can get
Not much scientific validity

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19
Q

Cross-sectional studies collect only which type of data?

A

Prevalence data

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20
Q

Uses of prevalence data

A

Describe health burden of a pop
Describe status of dz in a pop
Estimate the frequ (prevalence) of exposure
Project healthcare needs of affected individuals

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21
Q

Can cross-sectional studies be both descriptive and analytic?

A

Yes

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22
Q

Type of question addressed in a descriptive cross-sectional study?

A

What is the prevalence of disease x or exposure y in a given pop?

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23
Q

Type of question addressed in an analytic cross-sectional study

A

Is exposure A associated with outcome B?

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24
Q

Characteristics of descriptive cross-sectional studies

A

Have no “a priori” hypothesis
Person, place, and time
Often exist just to discover or describe the prevalence of various factors in the pop

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25
Q

Characteristics of analytic cross-sectional studies

A

Answer a research question about the association between an exposure and outcome variable
There is an “a priori” hypothesis.

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26
Q

Target pop definition

A

The pop about which information is desired

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27
Q

Source pop definition

A

The larger pop from which the sample was drawn
All members of the source pop had some opportunity to be in the study

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28
Q

Sample or study pop definition

A

The pop that is actually included in the analyses

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29
Q

What analysis is used when using categorical data?

A

Prevalence ratios
Prevalence odds ratios

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30
Q

a + c in the 2x2 table

A

all with the outcome

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31
Q

b + d in the 2x2 table

A

all without the outcome

32
Q

a + b in the 2x2 table

A

all exposed

33
Q

c + d in the 2x2 table

A

all not exposed

34
Q

Prevalence ratios definition

A

The ratios of the prevalence of dz in the exposed compared to the prevalence of dz in the non-exposed

35
Q

Prevalence ratio formula

A

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

36
Q

What does prevalence ratio (PR) = 1 indicate?

A

The outcome is equally common in those who have and do not have the exposure (implies no relationship between exposure and outcome)

37
Q

What does PR>1 indicate (assuming statistical significance?)

A

Means the outcome is more common in those who have the exposure (possible risk factor)

38
Q

What does PR <1 indicate (assuming statistical signficance?)

A

Means the outcome is less common in those who have the exposure (possible protective factor)

39
Q

Example of wording for a precise interpretation of a prevalence ratio

A

The prevalence of the dz (or outcome) in the exposed was XX times the prevalence of the dz in the not exposed

40
Q

What can cross-sectional studies generate?

A

Hypotheses

41
Q

What is one limitation to an analytic cross-sectional study?

A

Time sequence impossible to establish with certainty
-There has been no actual lapse of time between measurement of exposure and dz
-This presents difficulties in distinguishing the exposures from the outcomes of the dz

42
Q

Advantages of cross-sectional studies

A

-Can estimate the prevalence of a health problem, which can indicate its magnitude and distribution, a source of descriptive statistics.
-Useful for program planning and justification
-Quicker and cheaper than some other study designs
-Involve the collection of data on individuals, which can later be aggregated, if desired.
-May generate new etiologic hypotheses for further study

43
Q

Disadvantages of cross-sectional studies

A

-Do not provide incidence data
-The impact of quickly emerging dzs may be missed
-Not efficient for the study of rare dzs or rare exposures
-Cannot determine time sequence of exposure and dz, and therefore, one cannot say that one variable “caused” another
-Prevalent cases of lethal dzs are all survivors

44
Q

What are two synonyms for case-control studies?

A

Retrospective study
Case-comparison study

45
Q

Can case-control studies be both descriptive and analytic?

A

No, just analytic

46
Q

Definition of analytic studies for this module

A

Attempts to identify causes or risk factors that explain health-related states or events, and tests specific “a priori” hypotheses often developed in descriptive studies.
There is a comparison of some kinds.
There is at least one exposure and one outcome.

47
Q

Distinguishing features of case-control studies

A

-Individuals with a particular dz or condition are selected for comparison with individuals in whom the dz or condition is absent.
-Looks for an association by comparing h/o exposure between a group of diseased individuals and a group of non-diseased individuals.
-Two separate samples
-Dz status is known at the beginning
-Retrospective

48
Q

What is another characteristic of a case-control study?

A

The outcome is always identified prior to the exposure.
-Involves grouping people as cases and controls, and investigating whether the cases are more or less likely than controls to have had past experiences, lifestyle behaviors, or exposures.

49
Q

From where can cases come?

A

Public health clinics
Physicians’ offices
Health maintenance organizations
Hospitals
Industrial and government sources (registries)

50
Q

From where can data be obtained?

A

Medical records
Personal interviews
Telephone surveys
Written questionnaires
Physical examinations
Laboratory examinations or tests

51
Q

What is the dependent or outcome variable in a case-control study?

A

Dz

52
Q

Requirements about dz characteristics

A

-The dz spectrum should be known
-The case definition should be take into account the stage of dz and be established before data collection, as well as person, place, and time characteristics.

53
Q

Requirements for controls

A

-Should look like the case participants with the exception of the dz
-Requires selection from the same source pop as the cases.
-Must be chosen independently of exposure status

54
Q

3 main sources of controls

A

Population-based (best): Can be a probability (representative) sample of those without the dz from the same source pop as the cases.
Downside: expensive
Same hospital as cases but different dz
Downside: no healthy controls
Family, friends, neighbors, coworkers, relatives of the cases
Downside: may be too similar to the cases

55
Q

How can bias occur with control selection?

A
  1. Selection of cases that are not representative
    -Only those receiving medical attention
    -Only cases that survive
  2. Selecting controls that did not come from the same source pop as the cases
  3. Unknowingly selecting controls (or cases) on the basis of exposure
  4. Differential response rates among cases and controls, with the possibility that controls (or cases) who did not participate are systematically different than those who did.
56
Q

Can data on more than one exposure be gathered in a case-control study?

A

Yes

57
Q

How can information about exposure status be gathered?

A

Medical records
Interviews
Questionnaires
Surrogates such as spouses, parents, siblings, or employers

58
Q

How can there be issues with recall biases?

A

Determining exposure status for cases and controls:
-Be aware of limitations in recall
-Both cases and controls my not recall accurately their past exposures
-Cases may have a vested interest in recalling more

59
Q

Types of questions asked in case-control studies

A

Among the cases, is an attribute more or less common than among the controls
Is the mean level of factor Y greater among cases than among controls

60
Q

A in the 2 x 2 case-control table

A

Exposed cases

61
Q

B in the 2 x 2 case-control table

A

Exposed controls

62
Q

C in the 2 x 2 case-control table

A

Unexposed cases

63
Q

D in the 2 x 2 case-control table

A

Unexposed controls

64
Q

A + C in the 2 x 2 case-control table

A

All cases

65
Q

B + D in the 2x2 case- control table

A

All controls

66
Q

A + B in the 2 x 2 case-control table

A

All exposed

67
Q

C + D in the 2 x 2 case-control table

A

All unexposed

68
Q

Cross product ratio:

A

AD/BC

69
Q

The ratio of the odds of dz among the exposed to the odds of the dz among the unexposed

A

(A/B) / (C/D)

70
Q

The ratios of the odds of exposure among the cases to the odds of exposure among the controls

A

(A/C) / (B/D)

71
Q

What does OR = 1 indicate?

A

Implies no association

72
Q

What does OR>1 indicate (assuming statistical significance)?

A

Suggests the exposure is a risk factor

73
Q

What does OR <1 indicate (assuming statistical significance?)

A

Suggests a protective factor

74
Q

Precise interpretation of odds ratio terminology

A

Cases with ______ had ____x the odds of _____ compared to the controls

75
Q

Advantages of case-control studies

A

Useful for etiologic studies, to study the causes (determinants of a dz)
Tend to use smaller sample sizes than cross-sectional surveys or cohort studies
Are usually of short duration
Cost-effective
The only studies useful for studies of rare dzs or outcomes
Useful for studies of dzs with long latency periods where it is impractical to wait for the outcome to occur in healthy people
Many risk factors can be studied simultaneously

76
Q

Disadvantages of case-control studies

A

Not useful for planning purposes
Cannot estimate dz frequency, such as prevalence or incidence
Difficult to study rare exposures
Can investigate only one dz outcome per study
Problem with possible recall bias
Problems with bias d/t the selection of the wrong cases or controls
Cannot establish sequence of events very well
-Therefore, not usually sufficient to establish cause-effect relationship between exposure and dz

Epidemiology (17 decks)

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