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828 > Cohort Studies and RR > Flashcards

Cohort Studies and RR Flashcards

1
Q

Confidence Interval

A
  • CI
  • CI is a range of values that are likely to cover the true parameter
  • Built around the point estimate
  • Point estimate +/- margin of error
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2
Q

How Confident?

A
  • Arbitrary decision
  • Levels: 90%, 95%, 99%
  • Since alpha is usually 5%, CI is usually 95%
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3
Q

Interpretation of 95%

A
  • Addresses the precision of the point estimate: indicates the range in which the true value lies with 95% confidence
  • Tells us whether the observed differences are statistically significant
  • Cane be used for hypothesis testing
  • CI can indicate whether the results are statistically significant or not
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4
Q

Difference in Means

A
  • Difference b/w means = 0 means no association (Ho is true)

- If 0 is not included in the 95% range of values, means that we can say they are statistically significant

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5
Q

Difference in Proportions

A
  • If RR or OR = 1, no difference between the proportions and the Ho is true
  • If 1 is not included with 95% confidence we can conclude that proportions in two different groups are different (statistically significant)
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6
Q

Width of CI

A
  • Indicates its precision (wider = less precise)
  • Affected by level of confidence (higher confidence, wider CI) and sample size (bigger size, smaller CI)

Need larger sample size for rarer outcome

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7
Q

Cohort Studies

A
  • Cohort: group of persons with similar characteristics

- Cohort study is analysis of a group of persons with similar characteristics studied over time

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8
Q

Two Types of Cohort Studies

A
  1. Prospective Cohort

2. Retrospective Cohort

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9
Q

Prospective Cohort

A

Cohort is assembled at the present time and followed up toward the future.

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10
Q

Retrospective Cohort

A

Cohort is identified and assembled in the past on the basis of existing records and is “followed” to present time.

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11
Q

Cohort V.S. RCT

A
  • Cohort selects subjects in the study groups

- RCT randomizes the subjects in study groups

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12
Q

General Steps in Cohort Study

A
  1. Formulate a research hypothesis
  2. Define a cohort based off study population
  3. Ascertain the exposure
  4. Select exposed and unexposed groups
  5. Determine the follow-up period
  6. Determine the outcome
  7. Measure the association between exposure and outcome
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13
Q

Risk Factors + Cohort Types

A
  • Common risk factors enroll a single large cohort: General population/subset of general population
  • Rare/unusual risk factors use a special exposure cohort
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14
Q

Selecting Unexposed Subjects

A
  • Free of exposure
  • Should be similar in all other factors to avoid confounding
  • Collection of information should be similar in exposed and unexposed group
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15
Q

Sources of Exposure Data

A
  • Records collected independently of the study
  • Information supplied by the subjects
  • Medical examination
  • Direct measurement
  • Potential problems: incomplete information, changes in exposure levels over time
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16
Q

Sources of Outcome Data

A
  • Should be complete, comparable, and unbiased
  • Sources: records, questionnaires, direction medication exam
  • Potential problems: applying same diagnostic criteria and procedures

DATA COLLECTION SHOULD BE SIMILAR IN BOTH STUDY GROUPS

17
Q

Cohort Advantages

A
  • Temporal relationship between the risk factors and diseases can be established
  • Can estimate the incidence of disease and risk
  • Can study multiple outcomes because of a single risk factor
18
Q

Cohort Disadvantages

A
  • Can be very expensive and time consuming
  • Not good for rare diseases or diseases with long latency
  • Lost to follow up can introduce bias
19
Q

When is a Cohort Warranted?

A
  • Rare or unusual exposures
  • When multiple effects of a single factor need to be evaluated
  • When exposure needs to be carefully quantified
  • When RCT is unethical
20
Q

When Cohort is NOT desirable

A
  • Diseases with long latency
  • Rare diseases
  • Multiple exposures are studied
21
Q

Evaluating Cohort Quality

A
  • How are the groups selected/defined
  • Was the data accurate and collected comparably
  • Was the follow up complete

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