Study Design – Flashcards
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Study designs
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are structured approaches to address specific research questions
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Study designs provide general guidelines for thinking about specific aspects of study conduct. including:
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- sampling populations - how to systematically collect various measurements - how to analyze the data sets
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When selecting a study design you should start with a good study question like
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- Is it relevant - Is it novel - is it feasible
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Three main types of study designs
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Descriptive, analytic, diagnostic
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Descriptive study design consist of
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survey and qualitative
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Analytic study design consist of
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experimental and observational
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Analytic experimental study design consist of
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Randomised (Parallel group) Randomised (Crossover) meta analysis
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Observational experimental study design consist
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cohort study, cross sectional, case-control study
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Observational studies have zero
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randomization associated with them
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In observational studies, investigators do not
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assign subjects to groups
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In experimental studies, investigators
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assign subjects to different groups
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Power is less in what type of studies
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observational which includes cohort, case control, cross sectional
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What questions are asked when spotting the study design?
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What is the aim of the study? If it is analytic, was the intervention randomly allocated? When were the outcomes determined?
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If the aim of the study is to simply describe a population (PO questions) then it is a
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descriptive study
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If the aim of the study is to quantify the relationship between factors (PICO or PECO questions) then it is a
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Analytic study
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Which type of study would you expect residents to perform?
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descriptive studies because of time constraints
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If the study is analytic and the intervention is randomly allocated then it is a
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randomized control trial
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If the study is analytic and the intervention is not randomly allocated then it is a
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observational study
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If the outcomes were determined after the exposure or intervention then it is a
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cohort study
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If the outcomes were determined at the same time as the exposure or intervention then it is a
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cross sectional study or survey
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If the outcomes were determined before the exposure or intervention then it is a
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retrospective
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Why are systemic reviews strong evidence
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they look for published data and unpublished data which makes them strong evidence
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What is the major issue with meta analysis?
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the lack of negative publications
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Why are opinions and reviews important?
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because the opinions of experts matters and u will be asked about it during journal clubs
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What are the differences between study designs?
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- how participants are sampled - when measurements are to be taken - How outcome variables are measured - Are there comparison groups involved
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Case reports
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an article that describes and interprets an individual case and often written in the form of a detailed story
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Case reports often will describe
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- unique cases that cannot be explained by known diseases or syndromes - cases that show an important variation of a disease or condition - cases that show unexpected events that may yield new or useful information - cases in which one patient has two or more unexpected diseases or disorders
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Case report advantages
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-very good for rare cases -inexpensive - dont require a lot of time - can help in the identification of new trends or diseases - can help detect new drug side effects and potential uses - educational: a way of sharing lessons learned
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Case reports help to
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build hypotheses
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With case reports there is no
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control. since there is no control group there is no statistical validity
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Case reports disadvantages
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- cases may not be generalizable - not based on systematic studies - causes or associations may have other explanations -can be seen as emphasizing the bizarre or focusing on misleading elements
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Case control studies will often use an
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odds ratio
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Case control studies are generally designed to estimate
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the odds of developing the studied condition or disease
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With case control studies you can determine if there is
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an associational relationship between the condition and risk factor
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with case control studies u want the the sample to reflect the population so you want
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there to be more controls than cases = cuts out confounding and bias
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Biggest case control study that was disproved is what?
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vaccines and autism
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Case Control advantages
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- good for rare diseases - less time needed to conduct the study - u can look at multiple risk factors - useful as an initial study to establish an association
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Case control disadvantages
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- reliance on recall or records to determine exposure status - cofounders - selection of control groups - potential bias: especially recall and selection
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Cross sectional study
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- examines relationship between diseases and other variables of interest as they exist in a defined population at a specific point in time - section is independent of exposure or disease - carried out for public health planning and for etiologic research
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cross sectional studies are also known as
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prevalence studies because they are good for prevalence
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Cross sectional study advantage
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- INEXPENSIVE and takes little time to conduct - NO LOSS TO FOLLOW UP - estimate prevalence because sample is usually taken from the whole population - many outcomes and risk factors can be assessed - useful for public health planning, disease etiology, generation of hypotheses
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Cross sectional disadvantages
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- difficult to make casual inference - Prevalence and incidence bias (Neyman bias) - it is only a snap shot, may get different results if another time frame had been chosen
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Cohort study is associated with
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relative risk
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Odds ratio is associated with
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case control
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Prospective Cohort
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exposure factors are identified at the BEGINNING of a study and a defined population is followed into the future
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Retrospective cohort
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past medical records for the defined population are used to identify exposure factors and compared with another group
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You get answers faster with case control versus cohort but case control studies
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are only valid in specific populations while cohort is valid in multiple populations
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Population is more defined in case control but in cohort, the population
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is much larger and varying
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Cohort advantages
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- subjects in cohorts can be matched, which limits the influence of confounding variables - standardization of criteria/outcome is possible - easier and cheaper than a randomized controlled trial
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cohort disadvantages
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- cohorts can be difficult to identify due to confounding variables - no randomization so imbalance in patient characteristics could exist - blinding/masking is difficult - outcome of interest could take time to occur
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Randomized controlled study does not eliminate confounding and bias but
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it evenly distributes those between the groups
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Randomized controlled study is a study in which
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there are two or more groups, one of which is a control group the treatment group receives the Tx under investigation and the control group receives either no treatment or standard of care treatment subjects are randomly assigned to all groups
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RCT - randomization helps avoid
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selection bias
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RCT- randomization increases the probability that
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differences between groups can be attributed to the treatment under study
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What is considered the gold standard for medical research
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RCT
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RCT advantages
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- good randomization will "wash out" any population bias - easier to blind/mask than observational studies - results can be analyzed with well known statistical tools - populations of participating individuals are clearly identified
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RCT disadvantages
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- EXPENSIVE in terms of time and money - LOSS TO FOLLOW UP attributed to treatment - Volunteer biases, the population that participates may not be representative of the whole - does not reveal causation
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Double blind study
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RCT in which neither the medical personnel nor the patients know which treatment group they are allocated to
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Double blind study advantages
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less bias
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Double blind study disadvantage
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test subjects may not be receiving active drug or may be receiving an active drug that isnt comparable to what is out on the market
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Crossover study advantages
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- all subjects serve as own controls and error variance is reduced - thus reduces sample size - all subjects receive treatment at least at some point during the study - blinding can still be maintained
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Crossover study disadvantages
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- all subjects receive placebo or alternative treatment at some point - washout period can be lengthy or unknown - cannot be used for treatments with permanent effects
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Washout period
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u have to make sure treatment A is out of their system until you can administer treatment B
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If you see p values and confidence intervals then it is a
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meta analysis
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Meta analysis
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a systematic objective way to combine data from many studies, usually from randomized controlled trials arrive at a pooled estimate of treatment effectiveness and statistical significance can also combine data from case control and cohort studies
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Meta analysis advantage
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- includes data from multiple randomized clinical trials - greater statistical power - confirmatory data analysis - greater ability to extrapolate to general population affected - considered an evidence based resource
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Meta analysis disadvantage
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- DONT INCLUDE NEGATIVE STUDIES - 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 populations
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Systematic review
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- uses a process to identify comprehensively all studies for a specific focused question, appraises the methods of the studies, summarizes the results, and presents key findings - also identifies reasons for different results across studies - cites limitations for current knowledge
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Systematic review process uses what type of literature?
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both published and unpublished
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Systematic review process has a clearly formulated
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research question
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Key disadvantage with meta analysis is that
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you can quantify the data but you cant qualify the data meaning u cant assess the quality
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Final results of systematic review process are placed in context which addresses issues such as
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quality of the study, impact bias, applicability of the findings
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Systematic review advantages
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- exhaustive review of the current literature and other sources - Less costly to review prior studies than to create a new study - less time required than conducting a new study - results can be generalized and extrapolated into the general population more broadly than individual studies -more reliable and accurate than individual studies - considered to be evidence based
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Which study design is considered to be evidence based?
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Systematic review
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Systematic review disadvantage
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-time consuming - may not be easy to combine studies - studies included may be of varying study designs but they should be studying the same outcomes -did each
