NR 503- FINAL STUDY GUIDE
Definitions of study designs: Chapter 10: Differentiate between the case-control and cohort
studies. Ask yourself, which is used when, and why.
Case-control = with the disease. Controls = without the disease. Case-Control has diseased
and non-diseased people.
Cohort study = exposed and non-exposed people. A cohort study differs from a case-control
study in that:
o Subjects are enrolled or categorized on the basis of their exposure status in a cohort
study but not in a case-control study
o Subjects are asked about their exposure status in a cohort study but not in a case-
control study
o Cohort studies require many years to conduct, but case-control studies do not
o Cohort studies are conducted to investigate chronic diseases, case-control studies are
used for infectious diseases
Primary prevention: Primary = Prevent (initial development)
Secondary prevention: (screening), cost-effective, early detection, existing disease
Tertiary prevention: reducing impact of disease
Case-Control:
* Examine the possible relationship of an exposure to a certain disease
* Identify group of individuals with the disease (cases)
* For comparison, gather a group of people without that disease (controls)
* Determine what proportion of the cases were exposed and were not
* Also determine what proportion of the controls were exposed and not
,* Text: Thus, in a case-control study, if there is an association of an exposure with a disease, the
prevalence of history of exposure should be higher in persons who have the disease (cases) than
in those who do not have the disease (controls).
* Ask yourself: Why is this important to the NP in primary care? How does this inform a
provider’s decision-making?
Cohort Studies: Chapter 13: Comparing Cohort and Case-Control Studies: See Figure 13-1
and 13-2 (busy pictures but hang in there)
Chapter 13 comparison of studies - important to review
Matching: Chapter 10: Text: A major concern in conducting a case-control study is that cases
and controls may differ in characteristics or exposures other than the one that has been
targeted for study.
Randomization: The point of randomization is to prevent any potential biases on the part of
the investigators/researchers. Text: Thus, the use of randomization is crucial to protect the
study from any biases that might be introduced consciously or subconsciously by the
investigator into the assignment process.
Bias: (selection bias) (source of cases) Issues related to generalizability; cases from a single
source less than desirable than if from multiple sources with a varying pool of cases. Ask
yourself, why?
Causality: Table 14-3: Using the Evidence in Developing Recommendations
TABLE 14-3 The Process for Using the Evidence in Developing
Recommendations on the Effectiveness of Prenatal Interventions
Stage I: Categorizing the Evidence by the Quality of Its Source.
(In each category, studies are listed in descending order of
quality.)
1.Trials (planned interventions with contemporaneous
assignment of treatment and nontreatment)
o a.Randomized, double-blind, placebo-controlled with
sufficient power appropriately analyzed.
, o b.Randomized, but blindness not achieved.
o c.Nonrandomized trials with good control of confounding,
that are well conducted in other respects.
o d.Randomized, but with deficiencies in execution or
analysis (insufficient power, major losses to follow-up,
suspect randomization, analysis with exclusions).
o e.Nonrandomized trials with deficiencies in execution or
analysis.
2.Cohort or case-control studies
o a.Hypothesis specified before analysis, good data,
confounders accounted for.
o b.As above, but hypothesis not specified before analysis.
o c.Post hoc, with problem(s) in the data or the analysis.
3.Time-series studies
o a.Analyses that take confounding into account.
o b.Analyses that do not consider confounding.
4.Case-series studies: Series of case reports without any
specific comparison group
Among other issues that must be considered in reviewing the evidence are
the precision of definition of the outcome being measured, the degree to
which the study methodology has been described, adequacy of the sample
size, and the degree to which characteristics of the population studied and
of the intervention being evaluated have been described.
A study can be well designed and carried out in an exemplary fashion
(internal validity), but if the population studied is an unusual or highly
selected one, the results may not be generalizable (external validity).
Stage II: Guidelines for Evaluating the Evidence of a Causal
Relationship. (In each category, studies are listed in
descending priority order.)
1.Major criteria
o a.Temporal relationship: An intervention can be considered
evidence of a reduction in risk of disease or abnormality
only if the intervention was applied before the time the
, disease or abnormality would have developed.
o b.Biological plausibility: A biologically plausible mechanism
should be able to explain why such a relationship would be
expected to occur.
o c.Consistency: Single studies are rarely definitive. Study
findings that are replicated in different populations and by
different investigators carry more weight than those that
are not. If the findings of studies are inconsistent, the
inconsistency must be explained.
o d.Alternative explanations (confounding): The extent to
which alternative explanations have been explored is an
important criterion in judging causality.
2.Other considerations
o a.Dose-response relationship: If a factor is indeed the cause
of a disease, usually (but not invariably) the greater the
exposure to the factor, the greater the risk of the disease.
Such a dose-response relationship may not always be seen
because many important biologic relationships are
dichotomous, and reach a threshold level for observed
effects.
o b.Strength of the association: The strength of the
association is usually measured by the extent to which the
relative risk or odds depart from unity, either above 1 (in
the case of disease-causing exposures) or below 1 (in the
case of preventive interventions).
o c.Cessation effects: If an intervention has a beneficial
effect, then the benefit should cease when it is removed
from a population (unless carryover effect is operant).
Definitions of study designs: Chapter 10: Differentiate between the case-control and cohort
studies. Ask yourself, which is used when, and why.
Case-control = with the disease. Controls = without the disease. Case-Control has diseased
and non-diseased people.
Cohort study = exposed and non-exposed people. A cohort study differs from a case-control
study in that:
o Subjects are enrolled or categorized on the basis of their exposure status in a cohort
study but not in a case-control study
o Subjects are asked about their exposure status in a cohort study but not in a case-
control study
o Cohort studies require many years to conduct, but case-control studies do not
o Cohort studies are conducted to investigate chronic diseases, case-control studies are
used for infectious diseases
Primary prevention: Primary = Prevent (initial development)
Secondary prevention: (screening), cost-effective, early detection, existing disease
Tertiary prevention: reducing impact of disease
Case-Control:
* Examine the possible relationship of an exposure to a certain disease
* Identify group of individuals with the disease (cases)
* For comparison, gather a group of people without that disease (controls)
* Determine what proportion of the cases were exposed and were not
* Also determine what proportion of the controls were exposed and not
,* Text: Thus, in a case-control study, if there is an association of an exposure with a disease, the
prevalence of history of exposure should be higher in persons who have the disease (cases) than
in those who do not have the disease (controls).
* Ask yourself: Why is this important to the NP in primary care? How does this inform a
provider’s decision-making?
Cohort Studies: Chapter 13: Comparing Cohort and Case-Control Studies: See Figure 13-1
and 13-2 (busy pictures but hang in there)
Chapter 13 comparison of studies - important to review
Matching: Chapter 10: Text: A major concern in conducting a case-control study is that cases
and controls may differ in characteristics or exposures other than the one that has been
targeted for study.
Randomization: The point of randomization is to prevent any potential biases on the part of
the investigators/researchers. Text: Thus, the use of randomization is crucial to protect the
study from any biases that might be introduced consciously or subconsciously by the
investigator into the assignment process.
Bias: (selection bias) (source of cases) Issues related to generalizability; cases from a single
source less than desirable than if from multiple sources with a varying pool of cases. Ask
yourself, why?
Causality: Table 14-3: Using the Evidence in Developing Recommendations
TABLE 14-3 The Process for Using the Evidence in Developing
Recommendations on the Effectiveness of Prenatal Interventions
Stage I: Categorizing the Evidence by the Quality of Its Source.
(In each category, studies are listed in descending order of
quality.)
1.Trials (planned interventions with contemporaneous
assignment of treatment and nontreatment)
o a.Randomized, double-blind, placebo-controlled with
sufficient power appropriately analyzed.
, o b.Randomized, but blindness not achieved.
o c.Nonrandomized trials with good control of confounding,
that are well conducted in other respects.
o d.Randomized, but with deficiencies in execution or
analysis (insufficient power, major losses to follow-up,
suspect randomization, analysis with exclusions).
o e.Nonrandomized trials with deficiencies in execution or
analysis.
2.Cohort or case-control studies
o a.Hypothesis specified before analysis, good data,
confounders accounted for.
o b.As above, but hypothesis not specified before analysis.
o c.Post hoc, with problem(s) in the data or the analysis.
3.Time-series studies
o a.Analyses that take confounding into account.
o b.Analyses that do not consider confounding.
4.Case-series studies: Series of case reports without any
specific comparison group
Among other issues that must be considered in reviewing the evidence are
the precision of definition of the outcome being measured, the degree to
which the study methodology has been described, adequacy of the sample
size, and the degree to which characteristics of the population studied and
of the intervention being evaluated have been described.
A study can be well designed and carried out in an exemplary fashion
(internal validity), but if the population studied is an unusual or highly
selected one, the results may not be generalizable (external validity).
Stage II: Guidelines for Evaluating the Evidence of a Causal
Relationship. (In each category, studies are listed in
descending priority order.)
1.Major criteria
o a.Temporal relationship: An intervention can be considered
evidence of a reduction in risk of disease or abnormality
only if the intervention was applied before the time the
, disease or abnormality would have developed.
o b.Biological plausibility: A biologically plausible mechanism
should be able to explain why such a relationship would be
expected to occur.
o c.Consistency: Single studies are rarely definitive. Study
findings that are replicated in different populations and by
different investigators carry more weight than those that
are not. If the findings of studies are inconsistent, the
inconsistency must be explained.
o d.Alternative explanations (confounding): The extent to
which alternative explanations have been explored is an
important criterion in judging causality.
2.Other considerations
o a.Dose-response relationship: If a factor is indeed the cause
of a disease, usually (but not invariably) the greater the
exposure to the factor, the greater the risk of the disease.
Such a dose-response relationship may not always be seen
because many important biologic relationships are
dichotomous, and reach a threshold level for observed
effects.
o b.Strength of the association: The strength of the
association is usually measured by the extent to which the
relative risk or odds depart from unity, either above 1 (in
the case of disease-causing exposures) or below 1 (in the
case of preventive interventions).
o c.Cessation effects: If an intervention has a beneficial
effect, then the benefit should cease when it is removed
from a population (unless carryover effect is operant).
