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Research Methods > Chapter 11 > Flashcards

Chapter 11 Flashcards

1
Q

What does a cohort study do?

A

Follows participants through time to calculate the rate at which new disease occurs and to identify risk factors for the disease.

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2
Q

What is a cohort?

A

A group of similar people followed through time together.

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3
Q

All cohort studies are:

A

Observational (not experimental).

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4
Q

What are the two measurement times in cohort studies?

A

1) An initial survey that determines the baseline exposure and disease status of all participants.
2)  One or more follow up assessments that determine how many participants have developed a new (incident) disease since the initial examination.

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5
Q

Knowing which exposures were present in individual participants before the onset of new disease allows for the identification of what?

A

Potentially causal exposures.

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6
Q

What are the three types of cohort studies?

A

1) Retrospective (Historic-cohort)
2) Prospective (future-oriented)
3) Longitudinal 

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7
Q

Any study that follows participants forward in time can be considered to be:

A

A prospective study.

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8
Q

What do retrospective and prospective cohort studies recruit participants based on?

A

Their exposure status;

One group is known to be exposed, the other group is known not to be exposed. (Best for uncommon exposures)

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9
Q

What do longitudinal cohort studies recruit participants based on?

A

Membership in a well-defined source population.

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10
Q

For retrospective and prospective cohort studies, the members of the two comparison groups should be _____ except for ______.

A

Similar; their exposure status.

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11
Q

What is the key difference between retrospective and prospective studies?

A

When the baseline measurements are established.

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12
Q

When is the baseline information established in retrospective cohort studies?

A

Uses documented baseline information collected at some point in the past and follows the cohort to another point in the past or to the present. (So old information from past, then compared to new information in present)

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13
Q

When is the baseline information established in prospective and longitudinal cohort studies?

A

Use newly collected baseline data about exposures and outcomes in the present and follow the cohort to some point in the future.

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14
Q

What should retrospective and prospective studies be able to demonstrate?

A

That the outcome of interest was not present in any members of the cohort at baseline.

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15
Q

Longitudinal studies may use two kinds of population:

A

1) Fixed population

2) Dynamic population (Open population)

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16
Q

What is a fixed population?

A

All participants start the study at the same time and no one is allowed to join later.

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17
Q

What is a dynamic population (open population)?

A

Participants join at any time (rolling admission) and may replace dropouts.

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18
Q

What is the time to follow up based on for dynamic populations?

A

Individual participants’ dates of enrollment rather than a fixed calendar date.

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19
Q

What are time series studies or panel studies?

A

A variation of longitudinal studies that measures the same individuals repeatedly over time.

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20
Q

A surveillance system that monitors a population over an extended period of time using continuous data uses what kind of study approach?

A

Cohort

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21
Q

A study that measures individuals randomly sampled from the same population at different points in times are using what kind of study approach?

A

Repeated cross-sectional surveys.

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22
Q

What is the first step for a prospective cohort study?

A

Identifying two accessible source populations:

1) Individuals with the exposure of interest
2) individuals without the exposure of interest

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23
Q

What is the first step for a retrospective cohort study?

A

Identifying a source of existing records that can provide baseline data of adequate quality.

24
Q

What is the first step for a longitudinal cohort study?

A

Selecting a source population

25
Q

Prospective and longitudinal cohort studies must decide on what?

A

How often follow up data collection will take place and how long the study will continue.

26
Q

What is a major problem in prospective and longitudinal cohort studies?

A

Loss to follow up of participants.

27
Q

What can researchers due to minimize loss to follow up of participants?

A

Providing motivation or incentives to maximize interest and minimizing the burden of participation.

28
Q

Once source populations have been identified what is the next step?

A

Making plans for data collection.

29
Q

Survey instruments and other assessments for cohort studies must establish what?

A

Exposure and disease status for all participants at baseline and at follow-up.

30
Q

What type of bias may be found in cohort studies and why?

A

Information bias, because exposed participants may be more thoroughly examined for disease than unexposed participants.

31
Q

A strong data management system for cohort studies must be established to do what?

A

To link baseline and follow-up data while maintaining the confidentiality of the information provided by participants.

32
Q

What is the incidence rate?

A

The number of new cases of disease in a population during a specified period of time divided by the total number of people in the population who are at risk during that period.
(# of new cases)/(# of at risk people)

33
Q

Which people are excluded from the denominator in the incidence rate?

A

People who already have the disease.

34
Q

What units do incidence rates usually use?

A

Per 1000 or per 10,000

35
Q

Where is person-time used?

A

A denominator for incidence rates in some cohort studies, especially for dynamic populations.

36
Q

What is person-time?

A

A way of accounting for individuals in the study population being observed for a different length of time. (can be expressed in unitd as person-years, person-months…etc.)

37
Q

What does censored mean?

A

Removed from analysis.

38
Q

Do units matter for incidence rate ratios and other measures that compare incidence rates?

A

No, as long as all incidence rates in the equation use the same units.

39
Q

What is excess risk (attributable risk)?

A

The absolute difference in the incidence rate. (Exposed - unexposed)

40
Q

What does the excess risk number represent?

A

The additional rate of disease in the exposed that can be attributed to the exposure.

41
Q

What is one reason why the exposed and unexposed population in a cohort study must be similar except for the exposure status?

A

Because the excess risk (AR) calculation assumes that the exposed would have had the same rate as the unexposed if they had not had exposure.

42
Q

What is the attributable risk percent (AR%)?

A

The proportion of incident cases among the exposed that are due to the exposure. (AR/incidence rate)

43
Q

What does the attributable risk percent number mean?

A

The result is the number of cases of disease in the exposed that could have been prevented if the exposure was removed.

44
Q

What is the most common measure of association for cohort studies?

A

Incidence rate ratio (IRR) (Also called rate ratio (RR), relative rate, risk ratio, and relative risk)

45
Q

What is the IRR or RR?

A

It compares the incidence rate among the exposed to the incidence rate in the unexposed.

46
Q

What is the point estimate for the RR calculated as?

A

RR= [a/(a+b)]/[c/(c+d)]

47
Q

If RR=1 (or close to 1) then:

A

The incidence rate was the same (or about the same) in the exposed and in the unexposed.

48
Q

If RR>1, then:

A

The incidence rate was higher in the exposed than in the unexposed, suggesting that the exposure was risky.

49
Q

If RR<1, then:

A

The incidence rate was lower in the exposed than in the unexposed, suggesting that the exposure was protective.

50
Q

When the entire 95% confidence interval is less than 1, the RR is _____ (significant/not significant) and the exposure is deemed to be _____ (risky/protective).

A

Significant; protective

51
Q

When the entire 95% confidence interval is greater than 1, the RR is _____ (significant/not significant) and the exposure is deemed to be _____ (risky/protective).

A

Significant;risky (it is a risk factor for disease)

52
Q

When the entire 95% confidence interval is operlaps 1, the RR is _____ (significant/not significant). What does this mean for the exposure?

A

Not significant; there is no association between the exposure and disease. (Check power calculations to ensure sample size was not too small)

53
Q

If RR=0.5, what would the report say?

A

Participants with the exposure were half as likely to develop the disease as those without the exposure.

54
Q

If RR=2, what would the report say?

A

Participants with the exposure were twice as likely to develop the disease as participants without the exposure.

55
Q

Name seven statistical tests that can be derived from a 2x2 table for cohort studies.

A

1) Incidence in the exposed
2) Incidence in the unexposed
3) Excess risk or attributable risk (AR)
4) Attributable risk percent (AR%)
5) Incidence rate ratio (IRR)
6) Confidence intervals for the incidence rate, AR, AR%, and RR
7) Chi-square statistics and its associated p-value.

Research Methods (25 decks)

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