Study Design Flashcards
case report
an article which describes and interprets individuals cases, often written as a detailed stop
case reports are often described as
- unique, unexplainable cases
- cases which show variation in disease
- cases which show unexpected event which yield useful info
- cases in which patentees have two or more unexpected disorders
case reports are considered……., but are also
the lowest level of evidence, but are also the first line o evidence
why are case reports important
where new issues and ideas emerge- form the base of the pyramid
a good case report
is clear about the importance of the observation being reported
if multiple case reports show the same thing..
the next step ma be a case-control study to determine if there is a relationship between the relevant variables
+ves of case report
- help with identification of new trends of diseases
- detect new drug side effects and potential uses
- educational
- identifies rare manifestations of diseases
-ves of case report
- cases may not be generalisable
- not based on systematic studies
- causes or associations may have other explanations
- could be focusing on misleading elements
case- control study
a study which compares patients who have a disease or outcome of interest with patient who do not have the disease or outcome of interest. Looks back retrospectively to compare how frequently the exposure to a risk factor is present in each group to determine the relationship between the risk factor and the disease
why are case-control study observational
no intervention is attempted and no attempt is made to alter the course of the disease.
goal of case-control
to retrospectively determine the exposure to the risk factor of interest from each of the two groups of individuals: cases and controls.
case-control studies are designed to determine
odds
odds=
positive cases/ negative cases
+ve of Case-control
- good for studying rare diseases
- less time needed to conduct the study because the condition or disease has already occurred
- lets you simultaneously look at multiple risk factor
- useful as an initial study to establish an association
- can answer questions that could not be answered through other study design e.g. smoking causing lung cancer
-ve of Case-control
- retrospective studies rely on memory- recall bias
- not good for evaluating diagnostic tests because its already clear that the cases have the condition and the controls do not
- can be hard to find a suitable control group
why are retrospective studies less useful
recall bias- more problems with data quality because they rely on memory and people with a condition will be motivated to recall risk factors
cohort study
where one or more samples are followed prospectively and subsequent status evaluations with respect to a disease are conducted to determine which initial participants exposure characteristics (risk factors) are associated with it
as cohort studies commence
outcome for participants in each cohort is measured and relationship with specific characteristic determined
+ve of cohort
- subjects can be matched (limiting confounding)
- standardization of criteria possible
- easier and cheaper than RCT
-ve of cohort
- hard to identify confounding variables
- no randomisation- imbalances in patient characteristics
- blinding/ masking is hard
- outcome of interest may takes years
randomisation
limits imbalances in patient characteristics
Randomised control trial
a study which randomly assigns participants into an experimental group or a control group.
The study is conducted and only expected diff between the control and experimental groups is the outcome variable being studied
only expected difference between groups in RCT
only expected diff between the control and experimental groups is the outcome variable being studied
+ve of RCT
- good randomisation will wash out population bias
- easier to blind
- results can be analysed with statistical tools
- populations of participating individuals are clearly identified
-ve of RCT
- expensive: money and time
- volunteer biases: the population that participates may not be representative
- does not reveal causation
- loss to follow- up attributed to treatment
Practice guideline
a statement produced by a panel of experts which outline current best current practice to inform health professional and patients in making clinical decisions
- produced after extensive review of the literature and is typically created by professional associations, government agencies, and or price organisations.
good guidelines clearly
define the topic, appraise and summarise the best evidence regarding prevention, diagnosis, prognosis, therapy, harm and cost-effectiveness; and identify the decision points where this information should be integrated
to keep practice guidelines accurate and relevant
they should be reviewed frequently and updated as necessary
+ve Practice guideline
- created by panels of experts
- based on professional published literature
- practical guidance for clinicians
- considered evidence based resources
-ve practice guideline
- slow to change or be updated
- not always available for niche topics
- expensive and time-consuming to produce
- recommendations might be affected by the type of organisation creating the guideline
systematic review
a document written by a panel which provides a comprehensive review of all relevant studies on a particular clinical or health related topic/ question. The systematic review is created after reviewing and combining al the info for both published and unpublished studies and then summarising the findings
+ve Systematic reviews
- exhaustative review of the current literature
- less costly to review prior studies than conducting a new one
- results can be generalised and extrapolated into general population more broadly
- more reliable and accurate than individual studies
- considered an evidence based resource
-ve Systematic review
- very time consuming
- may not be easy to combine studies
process of writing a systematic review
1) identify the issue and determine the question
2) write a protocol
3) screen for studies
4) sift and select studies
5) extract data from the studies
6) assess the quality of the studies
7) combine the data
8) discuss and conclude overall findings
9) systematic review
10) dissemination
Meta-analyses
a subset of systematic reviews, a method for systemically combining pertinent qualitative and quantitative study data from several selected studies to develop a single conclusion that has greater statistical power
- this conclusion should be statistically stronger than the analysis of any single study
why are meta-analyses statistically stronger than the analysis of any single study
due to increased number of subjects, greater diversity among subjects, or accumulated effects and results
when should meta-analyses be used
- to establish statistical signify with studies with conflicting results
- develop more correct estimate of effect magnitude
- to provide a more complex analysis of harms, safety data and benefits
- examine subgroups with individual number that are not statistically significant
if systematic and meta-analyses group …….. they would be the highest level of evidence on the evidence hierarchy
RCT
+ve Meta-analysis
- greater statistical power
- confirmatory data analysis
- greater ability to extrapolate to general pop affected
- considered an evidence based resource
-ve Meta-analysis
- difficult and time consuming to identify appropriate studies
- not all studies provide adequate data for inclusion and analysis
- requires advanced statistical techniques
- heterogeneity of study population
