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Fundamentals of Epidemiology > Goals of Analytical Studies; Populations: Target, Source, and Study; Cross-sectional and Ecologic Studies > Flashcards

Goals of Analytical Studies; Populations: Target, Source, and Study; Cross-sectional and Ecologic Studies Flashcards

1
Q

What is the main objective of case reports and case series?

A

To provide a comprehensive and detailed description of the case(s) under observation. This allows other physicians to identify and potentially report similar cases from their practice, especially when they share geographic or specific clinical characteristics.

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2
Q

What is ecologic fallacy?

A

In an ecologic study you may be scribing to members of a group some characteristic that they do not possess as individuals.

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3
Q

What is an ecologic study?

A

A study of group characteristics, missing individual data. But these studies are still of value, they can suggest avenues of research that may be promising in casting light on etiologic relationships.

Distinguished by the fact that groups are the unit of observation/analysis

EX: per capita sugar consumption in Europe, age-adjusted prostate cancer mortality rate, average dietary fat intake per year in Maryland from 2000-2010

It examines rates of outcome in relation to a population-level exposure factor

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4
Q

What are the uses of descriptive epi?

A

Public Health Planning: How many people are affected? How important is a health problem to individuals and society? Does the problem merit resources and risks of intervention?

Generate hypotheses about determinants: How do patterns of the occurrence of the public health problem vary by different characteristics?

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5
Q

What are the uses of analytical epi?

A

Evaluating hypotheses: like is cigarette smoking associated with increased incidence of cervical cancer?

Evaluating interventions for managing disease: Among heart attack survivors, does taking low-dose aspirin daily decrease risk of a subsequent heart attack?

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6
Q

What is the target population?

A

The population about which inferences are desired.

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7
Q

What is the source population?

A

The source of subjects for a particular study, subset of target population, can be enumerated

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8
Q

What is the study population?

A

selected from the source population, the subjects who actually participate in study

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9
Q

What is internal validity?

A

Was the study done well? Are the findings valid? Does exposure A really cause an increased risk of disease B in our population?

Consider: Were there any major methodological problems? Could the findings be due to bias, confounding, random error?

You need to establish sound internal validity before you consider generalizing the results beyond the study population.

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10
Q

What is external validity?

A

Aka “generalizability” or “applicability” to target population

To what extent can the results obtained in the study be generalized or applied to other people at risk for the outcome of interest?

Need to examine characteristics of study participants, and who did NOT participate in the study

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11
Q

Give some examples of exposures and outcomes in epidemiologic research.

A
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12
Q

Explain these units of observation: group (of individuals) as unit, individual as unit

A

1) EX: class of registered students, city, country, ecologic study

2) EX: person or event (e.g. pregnancy)

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13
Q

Explain experimental allocation of exposure under study.

A

performed by researcher, may or may not be random

EX: clinical trial

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14
Q

Explain non-experimental allocation of exposure under study.

A

By nature, self-selection, imposed by others, etc.

Researcher does not want to/cannot interfere with exposure allocation

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15
Q

Explain data collection over time (timing of observations).

A

longitudinal recording of exposures and outcomes over time, data collected at least two time points

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16
Q

Explain data collection at one point in time (timing of observations).

A

exposures, outcomes, other factors collected at the same time point, cannot establish temporal sequence

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17
Q

How do you sample the source population?

A

1) By exposure status: exposed vs. unexposed (EX: cohort study)

2) by outcome status: disease vs. no disease (case vs. control) (EX: case-control study)

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18
Q

draw the web for epidemiologic study designs

A
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19
Q

What is the basic protocol in an ecologic study?

A
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20
Q

What are the advantages of ecologic studies?

A

Can usually be completed relatively quickly, if based on available data

inexpensive, if data are publicly available

good for hypothesis generation

can examine wide range of exposure levels, including ecologic/contextual exposures

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21
Q

What are the limitations in ecologic studies?

A

individuals who are exposed may not be the same as those with relevant outcome

can be difficult to interpret, as data are crude by nature

cannot establish temporality or causation

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22
Q

What is a cross-sectional study?

A

Observational/non-experimental study

Individual is unit of observation

Data collected at one single point in time from defined population (data collected on exposures, outcomes, other factors)

participants are most often selected without regard to exposure or outcome status

“snapshot” in time

often used as basis for public health policy and programming decisions

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23
Q

What is the basic protocol in a cross-sectional study?

A
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24
Q

What are the advantages of cross-sectional studies?

A

generate inferences and hypotheses

quick

low cost

highly generalizable, when based on sample of general population

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25
Q

What are the limitations of cross-sectional studies?

A

cannot establish temporality or determine causation

healthy worker effect

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26
Q

What is a clinical trial?

A

Controlled study that prospectively evaluates the effect of an allocated exposure (i.e. intervention) on the outcome of interest

All participants are “at risk” for outcome at baseline (study beginning)

effects in which we’re interested: efficacy and safety

considered “gold standard” of studies for interventions

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27
Q

What is the key experimental design of clinical trials?

A

Follow participants over time, collect data from at least two time points (e.g. before and after exposure (intervention))

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28
Q

What is the “big question” behind clinical trials?

A

Could differences in interventions elucidate why/how some people will develop the outcome(s) in the future while other people will not?

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29
Q

When can a clinical trial be justified?

A

When equipoise exists. Equipoise is a legitimate uncertainty or indecision as to choice or course of action because of an unknown balance of benefits and risks

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30
Q

What’s the general inclusion criteria of a clinical trial?

A
  • able to provide informed consent
  • at high risk for main outcome
  • at low risk for adverse side effects
  • likely to adhere to treatment and data collection/study procedures
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31
Q

What is randomization?

A

The use of chance to determine the assignment of participants to exposures (interventions)

the probability is pre-determined and known, a scientific method

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32
Q

Why randomize exposure allocation?

A

ensures that exposure assignment is unbiased

produces similar groups at baseline by known and unknown factors

goal: the only difference between the groups at the end of the study will be the result of the exposure/intervention

minimizes the threats of selection bias and confounding

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33
Q

What is a confounding variable?

A

A factor that can influence the outcome of an experiment, leading to inaccurate conclusions. Can increase variance and introduce bias

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34
Q

Explain the implication of confounding by indication in observational studies

A
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35
Q

What is a factorial design in a clinical trial?

A

It allows investigators to obtain evidence about efficacy from fewer patients that would be needed if A and B were individually tested in two separate trials, can test the effects of more than one treatment in a clinical trial.

Can also test for treatment synergy. Is the effect of the combined treatment different than expected based on the effects of the treatments alone?

36
Q

What is a crossover trial study design?

A

Two or more treatments are provided to subjects at different time periods, and the sequence of treatments is randomized for each subject. Each participant serves as their own control which creates comparability between treatment groups. Treatment should be followed by a “washout” period.

37
Q

When is a crossover trial feasible?

A

When outcomes are recurrent and no “carryover” treatment effect after “washout” period

38
Q

What is masking (blinding) in epi?

A

Procedures intended to keep participants in a study from knowing some facts or observations that might bias or influence their actions or decisions regarding the study. Masking subjects to exposure assignment minimizes information bias.

39
Q

What is a placebo?

A

An inactive or inert intervention or agent that is given as a substitute for the treatment and where the participant is not informed they’re receiving the active or inactive intervention.

40
Q

Why use a placebo in masking?

A

Equalizes psychological effects of an “intervention” aka placebo effect

41
Q

What is partial masking?

A

In some circumstances masking of participants and/or physicians may be impossible or unethical like behavioral modification. In this setting, others can generally still be masked like data collectors, adjudicators, laboratory measurements, and data analysts.

42
Q

What are the advantages of clinical trials?

A

“gold standard” of epi studies

can directly measure outcome incidence

designed to minimize bias

“highest” quality evidence available

can establish temporal sequence

43
Q

What are the challenges of clinical trials?

A

Cost

hard to find and recruit the right participants

ethical challenges

need for tremendous documentation, cost

may take years for outcomes and/or adverse events or develop

adherence and unplanned crossovers

44
Q

What is ascertainment in clinical trials?

A

In clinical trials it’s the process of capturing all outcomes of interest. This occurs when the probability of detecting a particular outcome or confition is influenced by factors other than the exposure or intervention of interest.

45
Q

What is a prospective/concurrent cohort study?

A

Participants are grouped based on exposure status at baseline and followed over time for outcome ascertainment

46
Q

What is a retrospective cohort study?

A

Both exposure and outcome assessment have already occurred when study is conducted; data collection on exposure and outcome are based on existing (historical) records but individuals are categorized by exposure status and are “followed-up” for outcome

47
Q

What is the basic protocol in a prospective cohort study?

A

1) obtain IRB approval
2) screen potential participants for study eligibility
3) enroll participants grouped by exposure status, all are “at risk” for outcome
4) gather baseline data from participants
5) follow participants over time collecting data on time-varying exposures (if applicable) and outcome(s)
6) conduct data analyses and report findings

48
Q

How do you characterize the exposure in a clinical study?

A

dichotomous exposure or ordinal/nominal exposure

49
Q

What kinds of exposures don’t change over time?

A

genetics at birth, birthplace, and race

50
Q

What kind of exposures change over time?

A

age, exposure to drugs, smoking patterns, diet, air pollution

51
Q

What sources of information are used to collect exposure data in cohort studies?

A
52
Q

Explain follow-up and outcome assessment in cohort studies

A
53
Q

How do you maximize participant retention in longitudinal studies?

A
54
Q

What is the primary objective for cohort study data analysis?

A

compare disease occurrence in exposed and unexposed groups through things like incidence rates and cumulative incidence

55
Q

Write a 2x2 table using shorthand notation for different cells

A
56
Q

How do you calculate cumulative incidence froma. 2x2 table?

A
57
Q

How do you cumulative incidence in exposed populations vs. unexposed?

A

With risk ratio (relative risk) and risk difference

58
Q

What are the steps to calculating risk ratio (RR)?

A

https://open.oregonstate.education/epidemiology/chapter/introduction-to-2x2-tables-epidemiologic-study-design-and-measures-of-association/

59
Q

What are the advantages of cohort studies?

A

efficient for rare exposures

can evaluate multiple effects of an exposure (i.e. can study more than one outcome)

can directly measure disease incidence or risk

for prospective design, good information on exposures, and clear temporal relationship of exposure preceding the occurrence of the outcome

For retrospective design, efficient for diseases that take a long time to develop

60
Q

What are the disadvantages of cohort studies?

A

inefficient for rare outcomes

expensive and time consuming (particularly for prospective design)

for prospective design, inefficient for diseases that take a long time to develop

for retrospective design, sometimes poor info on exposures and other key variables

61
Q

What is a case-control study?

A

Observational epidemiologic study of persons with the outcome of interest (“cases”) and those without (“controls”) that compares the presence of particular attributes (“exposures”) in the two exposures

Participant defined and selected by outcome status, then exposure(s) of interest are assessed and compared between cases and controls

62
Q

What are the key parameters of case-control studies?

A

individual is a unit of observation

observational design

participants selected based on outcome status, then exposures are assessed

follow-up of participants over time: population-based no, nested within a cohort study yes

63
Q

What is the big question addressed with case-control studies?

A

Could differences in outcome status help differentiate past exposure status? In other words, compare offs of exposure in cases to odds of exposure in controls

64
Q

How do you calculate odds of exposure?

A

Odds of exposure = (ability of exposure)/(1 - probability of exposure)

65
Q

What is a population-based case control study?

A

participants identified from a source population (that is not a cohort study), no pre-existing study infrastructure

66
Q

What is a nested case control study?

A

source population is ongoing cohort study, benefits of cohort design (e.g. well-defined exposure)

67
Q

What’s the basic protocol in a case-control study?

A

1) obtain approval of Institutional Review Board (IRB)
2) Screen potential participants for study eligibility
3) identify and enroll cases and controls, i.e., enroll individuals based on disease/no disease status
4) gather data on exposures
5) conduct data analyses and report findings

68
Q

How do you select cases for individuals with the disease for case-control studies?

A

Ideally you want to include those with “recent” occurrence of disease - new cases (want to see if exposure(s) are associated with developing disease as opposed to living with the disease)

goal: accurate classification using signs and symptoms, physical and pathological exams, results of diagnostic testing

Cases are selected independent of exposure status!

69
Q

How do you select cases in terms of sources of case identification for case-control studies?

A

hospital/clinic patient rosters, death certificates, special surveys (like NHANES), special reporting systems (birth and death registries)

Each source has dis/advantages

Goal: to identify as many true cases as possible (and as affordably and quickly as possible)

70
Q

How do you select the controls in a population-based case-control study?

A

individuals without the disease: a sample of the source population that produced the cases

cases and controls from the same source population so a member of the control group who had gotten the disease would have ended up being a case in a study

controls are selected independent of exposure status!

71
Q

what are the sources of control identification in a case-control study?

A

population, hospital/clinic, deceased individuals, case’s friends, spuse, and relatives

each source has dis/advantages

remember: if a member of the control group actually had the disease, would s/he end up as a case in the study?

72
Q

How do you increase the statistical power (detecting an association between exposure and outcome if one really exists) of an case-control study?

A

increase the size of the control group up to a ratio of 4 controls:1 case

beyond 4:1. not considered worthwhile due to increased costs with limited increase in power

73
Q

How do you select controls in a nested case-control study?

A

select cases and controls from an existing cohort study

Incidence density sampling: controls are selected from risk-set of individuals without the outcome at each time a case develops, control(s) selected for a case can become future cases!, each case-control pair has the same duration of risk of outcome (time at risk is a matching factor)

74
Q

What are challenges in case-control studies?

A

Cases and controls may differ with respect to characteristics other than the exposure targeted. Is study finding due to differences in exposure, or due to other differences between cases and controls?

Solution via study design: Match cases and controls for factors about which you’re concerned (but not targeting in your study)

75
Q

What is matching?

A

process of selecting the controls so they are similar to the cases with respect to certain characteristics (e.g. age, race, sex)

76
Q

What is individual matching? (case-control)

A

For each case, at least one control is selected who is similar to the case for the characteristic(s) of concern (but not the exposure(s) in study!)

EX: selecting controls in a nested case-control study where cases and controls are matched on duration time at risk

77
Q

What is group matching? (case-control)

A

Percentage of cases with certain characteristic(s) is identical to the percentage of controls with the same characteristic (e.g. if cases/controls are matched on sex, then P% of cases and P% of controls are male)

78
Q

What are problems with matching? (case-control)

A

Practical: a lot of matching may make it impossible to find a suitable control

Conceptual: once you match controls to cases by a certain characteristic, then you cannot study that characteristic in your analysis

So, only match on factors you are convinced are risk factors for the disease (and you therefore don’t need to investigate, but want to account for in the study)

79
Q

What are some sources of exposure information?

A
80
Q

Explain limitations in recall and how that can effect a study.

A

Virtually all people are limited to varying degrees in their ability to recall information. When this limitation affects data on exposures collected in a study, misclassification results. Misclassification leads to an overestimation or underestimation of the association between exposure and outcome.

81
Q

What is recall bias?

A

Non-differential recall of past exposures between cases and controls: leads to underestimation association between dichotomous exposure and an outcome (biases results towards the null hypothesis of no association)

Differential recall of past exposures between cases and controls: Different by amount and/or accuracy of recall, either underestimates (toward null) or overestimates (away from null) exposure and outcome association

82
Q

What is the data-analysis approach in a case-control study?

A

Compare the odds that a case is exposed to the odds that a control is exposed where odds = the probability of being exposed divided by the probability of being unexposed

83
Q

How do you compare odds of exposure in cases vs. controls

A

Odds ratio = (odds of exposure in cases)/(odds of exposure in controls)

84
Q

What are the advantages of population-based case-control studies?

A

efficiency: less time and money than cohort studies. experimental studies

efficient for rare diseases

efficient for diseases that take a long time to develop

can evaluate multiple exposures in relation to outcome (so, good for diseases about which little is known)

85
Q

What are the disadvantages of population-based case-control studies?

A

inefficient for rare exposures

sometimes difficult to establish temporal relationship between exposure and outcome

may have poor info on exposures because of retrospective nature

vulnerable to recall bias because of retrospective nature

86
Q

How do you interpret risk ratio/relative risk?

A

“The risk of [disease] was [RR] times as high in [exposed] compared to [unexposed] over [x] days/months/years”

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