Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

EPI > EPI Final > Flashcards

EPI Final Flashcards

1
Q

Cohort study limitations

A
  • need large numbers of subjects to be followed long periods of time so logistically difficult
  • time consuming and expensive
  • loss to follow has potential to undermine validity
  • not good for rare diseases or those with long latency
  • not good when exposure data are expensive to obtain
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Why conduct a case-control study?

A

Reduced size of study greatly reduces costs. If sampling done properly, we’ll get the correct value for the measure of association.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

When is it desirable to conduct a case-control study?

A
  • when exposure data are expensive or difficult to obtain
  • when disease has long latent period
  • when disease is rare; cohort study would require too large of a sample size
  • when population is difficult to follow
  • when little is known about the disease
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

selecting cases for case-control studies

A
  • must have clear case definition
  • cases can be identified from a variety of places
  • cases are the same as those that would be included in a cohort study
  • cases are statistically precious– enroll as many of them as possible
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

issues in selecting case-control cases

A
  • cases should preferably be new (incident cases)
  • DO NOT choose prevalent cases since prevalence influence both whether disease occurs and how long it lasts
  • will not be able to distinguish exposure to relative occurrence of new disease and its duration
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

case-control controls

A

def: a sample of the source population that produced the cases

purpose: to estimate the exposure distribution in source population that produced the cases

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Control selection

A
  • controls must come from the same source population as the cases through random selection to represent the source population
  • controls must be selected independently of exposure
  • ask yourself the would citerion
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

nested controls

A

def: controls selected from an existing cohort population; represents a subset of the full source population

good: controls come from clearly defined source population

bad: restricted to members of existing cohort; may limit hypothesis that can be studied

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

population-based controls

A

def: controls selected from the general population, most suitable when cases are from well-defined geographic area

sources: random digit dialing, cellphone subscribers, residence lists, voter registration

good: controls often come from well-defined source population

bad: very time consuming, harder to inspire participation, may not recall past exposures as well as cases

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

hospital or clinic based controls

A

def: controls selected from among patients at a hospital or clinic

selection: choose control patients with diseases other than the case’s disease; typically used when cases are identified from a hospital

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

requirements of a hospital based control

A
  • same source population as cases: must consider the “would criterion” and the referral pattern
  • illness should be unrelated to, that is, independent of the exposure under study
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What illnesses make good hospital controls?

A
  • illnesses that have the same catchment area as the cases
  • illnesses that have no relation to the risk factors under study
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Good news about hospital controls

A

easy to identify and access, less time and money, accuracy of exposure recall comparable to cases, more willing to participate

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Bad news about hospital controls

A

These controls are not randomly selected. This means that hospital-based controls must be carefully selected to accurately represent the exposure history in source population

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Ratio of controls to cases

A
  • when the number of available cases is limited and controls are relatively plentiful, it is possible to increase the power of the study to detect an association by increasing the size of the control group
  • control-to-case ratios of up to 4 to 1 help to increase power\
  • ratios higher than this are not considered worthwhile
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

survival sampling

A
  • cumulative case-controls correspond to cohort studies that follow a closed population and measure risks, rather than rates
  • controls are sampled from the entire source population of non-cases at the end of follow-up
  • when disease is rare, there is no overestimation
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

risk set sampling

A
  • incidence density “selects” from the risk set during the same follow-up period in which cases are identified; that is, the probability of selection is proportional to the time at risk
  • control is sampled from the set of people in the source population who are at risk for disease at that time
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

case-cohort sampling

A
  • controls are sampled from the list of all people in the source population at risk for the outcome at the beginning of follow-up without regard for their exposure status, and regardless of whether they became cases after the start of follow-up
  • thus some controls may also be cases as each person has the same chance of being included in the study as a control
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

case-control studies strengths

A
  • fewer ethical concerns than experimental studies
  • more efficient than cohort study
  • requires less time and money, fewer subjects
  • no need to wait for long-latency diseases to develop
  • easy to explore effect of many exposures on an outcome
  • useful for disease with little information
  • important for infectious disease outbreak investigations
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

case-control limitations

A
  • often limited to studying a single outcome
  • inefficient for rare exposures
  • more opportunity for systematic bias
  • may be unsure about temporal sequence between exposure and disease
  • cannot calculate absolute measure of association
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

Direction of bias: towards the null

A
  • Positive associations is biased towards the null value. True association is underestimated.
  • Preventive association is biased towards the null value. True association is underestimated.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

Direction of bias: away from the null

A
  • Positive association is biased away from the null value. True associations is overestimated.
  • Preventive association is biased away from the null value. True association is overestimated.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

Selection bias

A
  • Def: bias that can occur if people who agree to take part in a study are different from the source population you want to study
  • selection bias has to do with WHO gets into your study
  • results from procedures used to select subjects into a study
  • leads to an observed association that differs from what would have been obtained from source population targeted for study.
24
Q

Selection bias on Case-control & Cohort

A
  • Case-control: selection of cases and controls is related to exposure status
  • Cohort/experimental: selection of exposed and unexposed subjects is related to disease status
  • more likely to occur in case-control or retrospective cohort studies because exposures and outcomes have already occurred by the time a subject is selected into a study
25
Q

Control-selection bias

A
  • Bias that can occur if controls are more likely to be selected if they are exposed
  • this bias occurs when controls fail to represent the exposure distribution in the source population from which the cases arose because controls do not accurately represent the same source population as the cases
  • effect: toward or away from null
  • prevention: use identical selection criteria for cases and controls
26
Q

Differential participation

A

Bias that can occur if willingness or ability to participate is related to both exposure and disease status
- effect: toward or away from null
- prevention: obtain high participation rates for all groups

27
Q

Differential loss to follow up

A
  • bias that can occur if study participants exit a study for reasons related to both exposure and disease
  • think of this type of bias as selection out of a study rather than entry into a study
  • prevention: since outcome cannot be known without good follow-up, must maintain high participation rates
28
Q

Reducing selection bias

A
  • little can be done to fix selection bias once it has occurred
  • selection bias must be avoided through careful study design and conduct
  • selection bias cannot be “controlled” in the analysis
29
Q

Information bias

A
  • bias that can occur if the information you collect from or about study participants is erroneous
  • has to do with the information that gets into your study
  • occurs after participants have entered a study
  • results form differences in the way information is obtained
  • leads to an observed association that differs from what would have been obtained if all study participants had been classified correctly
30
Q

Information bias on case-control study

A

different techniques are used to collect information from cases and controls
- information bias is more likely to occur in case-control or retrospective cohort studies because exposures and outcomes have already occurred by the time a subject is selected into a study

31
Q

Information bias on cohort study

A

different procedures are used to collect information from exposed and unexposed groups

32
Q

Recall bias

A

bias that can occur if people with disease remember/report their exposure differently than people without the disease

33
Q

Recall bias on case-control study

A

cases are more or less likely to recall prior exposures than controls

34
Q

Recall bias on retrospective study

A

exposed participants are more or less likely to recall prior diseases than unexposed participants

35
Q

Recall bias solutions

A
  • use controls who are also sick to promote comparable recall
  • use standardized, closed-ended questionnaires to promote consistency and specificity
  • examine pre-existing data or use biological measurements to ascertain exposure
36
Q

Interviewer bias

A

bias that occur if there is a systematic difference in soliciting, recording, or interpreting information

37
Q

Interviewer bias on case-control study

A

interviewer is influenced by participation’s case or control status

38
Q

Interviewer bias on cohort study

A

interview is influenced by participant’s treatment or exposure status

39
Q

Interviewer bias solutions

A
  • use blinding/masking to prevent interviewers to study hypothesis or to knowing whether someone is exposed
  • examine pre-existing data
  • provide adequate and rigorous training for interviewers
40
Q

Measurement error (misclassification)

A

bias that can occur if study participants are placed into the wrong exposure or disease category

41
Q

Misclassification error sources and effect

A
  • self-reoorts
  • errors on medical records, death certificates, etc.
  • errors in how data are captured
  • non-specific disease or exposure definitions

effects:
non-differential –> bias towards the null
differential –> bias towards or away from null

42
Q

Non-differential misclassification

A

the extent of the misclassification is the same for both groups
- if exposure is the thing being misclassified, then the extent of the exposure misclassification is the same for cases/controls or diseases/non-diseased
- if disease is the thing being misclassified, then the extent of the disease misclassification is the same for exposed and unexposed persons

43
Q

Non-differential misclassification of exposure

A

if exposure is the thing being misclassified, then the extent of the exposure misclassification is the SAME for cases/controls or diseased/non-diseased

44
Q

Poor recall vs recall bias

A
  • poor recall happens all the time
  • recall bias occurs only when recall is different for people who do and do not have the disease ( 90% of cases and 70% of controls accurately recall their exposure) –> AWAY from null
  • poor recall is a form of non-differential misclassification (90% of the cases and 90% of the controls accurately recall their exposure) –> TOWARDS the null
45
Q

Misclassification solutions

A

improve accuracy of collected information:
- use most accurate source of information available
- multiple measurements of exposure and disease
- validation–corroborate the data using several sources

46
Q

reducing information bias

A
  • little (or nothing) can be done to fix information bias once it has occurred
  • information bias must be avoided through careful study design and conduct
  • information bias cannot be “controlled” in the analysis
47
Q

confounding

A

systematic difference between the groups compared that distorts the true association between an exposure and disease

48
Q

sources of confounding

A
  • experimental and cohort studies: occurs when the exposed and unexposed groups differ by more than just the exposure–they differ by some other variable
  • case-control study: occurs when cases and controls have different characteristics
  • can occur in all types of epidemiological studies
  • unlike bias, it is an inherent characteristic of the population
49
Q

effects of confounding

A
  • results in a distortion of the true association between an E and D. Can bias either towards or away from the null
  • can be adjusted for to a point
50
Q

How is confounding related to the counterfactual ideal

A
  • confounding occurs when the risk of disease in the unexposed group does not equal the risk of disease the exposed group had they been unexposed
  • this means that the difference in disease risk between the exposed and unexposed group is due to factors other than just the exposure
51
Q

When is a variable a confounder?

A

Three criteria:
- independent predictor of the outcome
- associated with the exposure
- cannot be an intermediate on the causal pathway between exposure and disease

52
Q

Randomization strengths and limitations

A

strengths:
- no limit on the number of confounders that can be controlled for
- do not need information about unknown confounder
- do not need to know what they are
- do not need to measure them

Limitations
- limited to experimental studies
- less effective with smaller sample size

53
Q

Restrition

A

limit study to people who are within one category of the confounder

strengths:
- simple–conceptually and practically
- effective control of characteristics being restricted

limitations:
- only possible for known, measured confounders
- incomplete control for confounding if restriction is not narrow enough
- cannot evaluate restricted variable
- limits sample size
- limits generalizability of results

54
Q

Matching

A

select study subjects so that confounders are distributed identically among the exposed and unexposed or case and controls

strengths:
- simple and effective control of characteristics being matched
- useful for variables that are complex or difficult to capture

limitations:
- only possible for known measured confounders
- can be difficult, expensive, and time-consuming to find appropriate matches
- cannot evaluate matched variable

55
Q

Stratification

A

separate your study population into subgroups where one group has the confounder characteristics and one group does not. Then calculate a measure of association for each subgroup

56
Q

Stratification strengths

A
  • straightforward and easy to perform
  • effective control of characteristics being stratified
57
Q

Stratification limitations

A
  • difficult to control for many confounders simultaneously due to sparse data problems
  • difficult presentation, esp. if many confounders
  • continuous variables not easily stratified

EPI (1 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2025 Bold Learning Solutions. Terms and Conditions