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Summary Epidemiology

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Summary study book Clinical Epidemiology of Grant S. Fletcher - ISBN: 9781975140984, Edition: Sixth, International Edition, Year of publication: - (Educational)

Voorbeeld 4 van de 35  pagina's

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  • 30 oktober 2021
  • 35
  • 2021/2022
  • Samenvatting
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Week 3: Epidemiological Research Design




Learning Objectives:

Description & Comparison of the strengths and weaknesses of the common epidemiologic

study designs

Classification & Basic characteristics of research methods

Evaluation of Levels of evidence

Interpretation of the study validity & the impact of bias, confounding, reliability and effect

modification on causal inference in epidemiologic research

Critical appraisal of epidemiologic research




Contents
Introduction ............................................................................................................................................ 1
Study Design ........................................................................................................................................... 3
Experimental studies........................................................................................................................... 3
Randomized Controlled Trial (RCT) ..................................................................................................... 4
Observational studies ......................................................................................................................... 5
Cohort study.................................................................................................................................... 5
Case-control study .......................................................................................................................... 7
Cross-sectional study ...................................................................................................................... 8
Basic research methodology and relevant design considerations ....................................................... 10
Hierarchy of evidence ........................................................................................................................... 12
Validity in Study Designs ....................................................................................................................... 14
Internal Validity ................................................................................................................................. 15
Selection bias ................................................................................................................................ 15
Information bias ............................................................................................................................ 17

, Confounding .................................................................................................................................. 19
Effect modification or Interaction................................................................................................. 21
Reliability....................................................................................................................................... 22
External Validity ................................................................................................................................ 24
Critical appraisal of epidemiological research ...................................................................................... 24
Applicability of epidemiological evidence/research in public health practice and policy................ 27
References ............................................................................................................................................ 29

,Introduction
The key consideration of descriptive epidemiology – shown in Week 1 and Week 2- is

evaluation of frequency and pattern of health outcome by examining the person, place, and

time in relation to health outcome. Analytical epidemiology builds up on it and uses data

gathered by descriptive epidemiology as to look for patterns suggesting causal relationships.

It has been said that epidemiology by itself can never prove that a particular exposure caused

a particular outcome. It is because establishing an association does not necessarily mean that

the exposure is a cause of the outcome, i.e. that it is something that has an effect or a

consequence. Still, establishing a valid association between exposure and outcome is a

necessary first step that must be accomplished before assessing whether the relationship is

causal. Since a determination that a relationship is causal is a judgment, there is often

disagreement, particularly since causality often implies some degree of responsibility for the

outcome, or may create a demand for public health action, and this often has legal and financial

consequences (LaMorte 2019a).

Irrespective of whether epidemiologists aim to study occurrence and distribution of diseases

and health outcomes or they plan to further examine associations or hypothesized causal

relationship between a particular exposure and a particular outcome, a first step is to define

the hypothesis based on the research question and decide which study design will be best

suitable to answer that research question. In Week 3 we will learn about study designs. In

continuation, we will define research methodology which is the way in which data are

collected and analysed (Fink 2012, p. 301). We will also define levels of evidence (hierarchy

of evidence) which are assigned to studies based on the methodological quality of their

design, validity, and applicability. Additionally, we will pay special attention to the concept

of validity, which highlights the need to eliminate or minimize the effects of extraneous

influences, variables, and explanations that might detract from a study’s ultimate findings.
1

, Finally, having these terms understood, one will be able to undertake a critical appraisal of

epidemiological research, that is to accurately assess the quality and relevance of evidence

presented in a paper and its applicability to decision making and recommendations in (public)

health practice.

Before embarking further into Week 3 topic, please find below terminology essential to

understanding of the concepts relevant to Week 3 (some terms were already introduced in

Week 2):

Baseline: The amount of a particular disease that is usually present in a community is referred

to as the baseline- note that it is the observed level and not necessarily zero (Dicker 2006).

Source population: the population out of which the cases arose.

Incident case: a person who is newly diagnosed as a case.

Prevalent case: a person who has a health outcome of interest that was diagnosed in the past.

Cause: To be a cause, the factor: i) must precede the effect, ii) can be either a host or

environmental factor (e.g., characteristics, conditions, actions of individuals, events, natural,

social or economic phenomena) and iii) may be positive (presence of a causative exposure) or

negative (lack of a preventive exposure) (LaMorte 2019a).

Random allocation: each subject under study has an equal chance of being assigned to any one

of the exposures.

Reliability: Implies that the same data would have been collected each time over repeated tests/

observations (not to be confused with accuracy).

Internal Validity: the extent to which the observed results represent the truth in the population

we under study and, thus, are not affected by methodological errors.



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