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Epidemiology > Analytical vs. Descriptive Studies > Flashcards

Analytical vs. Descriptive Studies Flashcards

1
Q

Types of Descriptive Studies

(3)

A
  • Case reports/series
  • Cross-sectional
  • Correlational (Ecologic)
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2
Q

Types of Analytical Studies

(4)

A
  • Prospective Cohort
  • Retrospective Cohort
  • Case-control
  • Randomized trials
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3
Q

Characteristics of Descriptive Studies

(4)

A
  • Relatively inexpensive
  • used when little is known about dz.
  • less time-consuming
  • easy to collect information
    • info already exists
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4
Q

Pro’s of Case Reports (Series)

A
  • Quick
  • Inexpensive
  • may be 1st indication of an epidemic or newly recognized dz.
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5
Q

Con’s of Case Reports (Series)

A
  • No control groups
  • Can’t generalize finidings
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6
Q

Characteristics of Cross-sectional Studies

(AKA Prevalence studies)

A
  • snapshot of health @ a defined point in time
  • Exposure & dz are assessed @ the same time
  • Used to quantify magnitude of a problem
  • Uses surveys
  • Incidence rate cannot be measured
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7
Q

Pro’s of Cross-sectional Studies

(4)

A
  • Quick
  • Easy
  • Inexpensive
  • Snap-shot
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8
Q

Cons of Cross-sectional Studies

A

Can’t assess cause & effect

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9
Q

Which study types looks at Herd Immunity?

A

Ecologic Studies

(Correlational; Aggregate)

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10
Q

How is an ECOLOGICAL FALLACY committed in Ecologic Studies?

A

by assuming that the association found @ herd level is also true on the individual level

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11
Q

Pros of an Ecologic Study

A
  • Observes patterns –> form hypotheses
  • Quick & cheap –> uses available info
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12
Q

Cons of Ecologic Studies

A
  • Can’t link exposure to dz.
  • Can’t control confouding factors
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13
Q

Goal of descriptive studies

A

to describe the occurrence of disease in populations & generate hypotheses

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14
Q

Goal of Analytical Studies

A
  • ID & explain the causes of disease
  • Quantify the effect of a potential risk (exposure) factor
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15
Q

Characteristics of Case Reports

A
  • Describes a single Case
  • May lead to the formulation of a new hypothesis
  • Often 1st report of a new disease
  • reported as a clinical narrative
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16
Q

What is the minimum number of cases needed to be a “case series”

A

5

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17
Q

Why are Cross-Sectional Studies often performed?

A

to quantify the magnitude of the problem (dz)

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18
Q

Use of a 2x2 Table

A
  • Most common way to measure the association bewteen an exposure factor (+ or -)

&

  • Occurrence or absence of dz.
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19
Q

What is a cohort?

A

a group of animals who share a common experience with a defined time

(ex. birth cohort, year entered vet school)

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20
Q

What is the best method in comparing disease INCIDENCE between 2 cohorts?

A

Cohort studies

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21
Q

Characteristics of Prospective Cohort Studies

A
  • Select exposed & non-exposed groups
  • Follow them forward & measure the amount of disease that occurs in each
  • Follow-up is from present to future
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22
Q

Characteristics of Retrospective (HX) Cohort Studies

A
  • Uses past reliable medical records
  • selects groups according to presence or absence of exposure
  • Traces groups to present to determine dz. or outcome status
  • follow-up is from past to present
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23
Q

Relative Risk Ratio (RR)?

A

the ratio of the probability of an event occurring (for example, developing a disease, being injured) in an exposed group to the probability of the event occurring in a comparison, non-exposed group.

24
Q

2 important features of Relative Risk Ratio

A
  • Comparision of risk between two “exposures” puts risks in context,
  • “exposure” is ensured by having proper denominators for each group representing the exposure
25
Q

If RR is close to 1 what does that mean?

A

The exposure is probably not associated with the risk of the dz

26
Q

If RR is greater or smaller than 1?

A

the exposure is likey to be associated with the risk of dz

27
Q

The greater the departure from 1 of the RR?

A

The stronger the association between the risk & the dz.

28
Q

How do you calculate RR?

A

Relative Risk =_ Incidence in the exposed_

                        Incidence in the unexposed

RR= 1, NO ASSOCIATION

RR > 1, (+) association, possibly causal

RR < 1, (-) association, possibly protective

29
Q

What do we use to determine the statistical significance of RR value?

A

Confidence intervals

30
Q

What is the confidence interval a measure of?

A

a measure of the reliability of an estimate.

31
Q

At what Confidence Interval is the RR statistically signifcant?

A

If the 95% CI DOES NOT include the null value of 1, but falls entirely on either side of it

32
Q

Strengths of Prospective Cohort Studies

(3)

A
  • measure incidence
  • describe temporal relationships
  • Can collect data on possible confounders (age, sex, breed, etc)
33
Q

Strength of Both Prospective & Retrospective Cohort Studies

A
  • Useful when exposure is rare
  • can examine the multiple likely outcomes/dz of a single exposure
34
Q

Weakness of Cohort Studies

A
  • Inefficient for rare diseases
  • requires good records
  • may lack data on confounders
  • selection bias
35
Q

Weakness of Prospective Cohort Studies

A
  • Expensive & long
  • large number of subjects are needed
  • loss to follow-up which can affect validity
36
Q

What happens in a Case-Control Study?

A
  • Cases & controls are selected
  • compare the frequency of exposure factors in the cases w/ that of the controls
37
Q

What are the cases in a case-control study?

A

those study subjects who have developed the dz of interest

38
Q

What are controls in a case-control study?

A
  • study subjects who have not developed the dz of interest at the time of selection

Key point: represent individuals whose exposure to the factor of interest reflects the exposure in the population from which cases were selected

39
Q

How do you select individuals for case-control studies?

A
  • Select a dz
  • get a case definition
  • have diagnostic criteria
40
Q

How do you select controls for a Case-Control Study?

A
  • should be similar cases
  • should be identical to cases in every respect except the dz of interest
  • “match” controls to cases on possible confounders (age, breed, sex)
41
Q

What ratio is used in Case-Control Studies?

A

Odds Ratio

(interpret as you would the RR)

42
Q

Strengths of Case-control Studies

A
  • Efficient for rare diseases or when long interval btwn exposure & dz.
  • able to evaulate multiple etiologies
  • inexpensive & fast
  • require relatively small number of subjects
43
Q

Some weaknesses of Case-Control Studies

A
  • cannot directly estimate incidence or prevalence
  • selection of controls can be difficult
  • recall bias from owner
  • temporal relationships between exposure & occurrence of dz are difficult to establish
44
Q

Purpose of Randomized Clinical trails

A

test the effect of new TX/prevention intervention

45
Q

Which study provides the strongest evidence of causality?

A

Clinical trails (intervention studies)

46
Q

Strengths of Non-observational studies

A
  • less opportunity for error
  • animals randomly allocated to avoid bias
  • measure the effect of a TX/prevention intervention after a certain time
47
Q

Which trail evaulates whether an agent or procedure reduces risk of dz developing in those currently free of dz?

A

Prevention Trials

(Field trial)

48
Q

Advantage of Trials?

A

use blinding to eliminate selcetion & observation bias

49
Q

List the different types of Trials

A
  • Open
  • Blinded
  • Double-blinded
50
Q

What is an Open Trial?

A

subject & investigator know who is assigned to which treatment group

51
Q

What is a blinded trial?

A

investigator knows but subjects are blind to TX assignment

52
Q

What is a Double-blinded trial?

A

Subject and investigators are blind to TX assigned

53
Q

Things to look for in a Published Clinical Trial

A
  • What were TXs compared to
  • were individuals randomly allocated
  • was double-blinding performed
  • Were withdrawals from the study reported
  • Stastical significane & power
54
Q

List & describe the Phases of Preventative (Prophylactic) Trial

A
  • Phase I - product safety is tested on a limited # of animals
  • Phase II - limited # of animals are vaccinated & then challenged
  • Phase III - large # of animals are vaccinated to estimate both efficacy & effectiveness of vaccine
55
Q

Strengths of Clinical Trials?

A
  • researcher has control
  • best measure of causal relationship
  • provides cause-effect data
  • randomized - less confounding & removes selection bias
  • Blinding - eliminates selection & observation bias
56
Q

Weakness of Clinical Trials

A
  • excessive control does not mean it accurately represents the real situation
  • requires a large sample size
  • costly
  • long duration
  • ethical consideration
  • bias may be introduced
57
Q

What should you look for when evaluating a therapy question?

A
  • Study randomized?
  • Double-blinded?
  • Follow up > 80%?
  • Was the study question answered?
  • How large was the TX effect?
  • Will results help my patient?
  • Were study patients similar to yours?
  • Are the benefits wortht the risk & cost?

Epidemiology (6 decks)

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