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Evidence Based Medicine > Types of Research Studies > Flashcards

Types of Research Studies Flashcards

1
Q

Why appraise?

A
  • many poor quality studies get published even in reputable journals
  • conclusions can be formulated based on weak or even non-existent data
  • “publication pressure” has resulted in “predatory journals” which often publish w/ v weak peer review policies
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2
Q

What is predatory publishing?

A
  • open access publishing business model (not all open access journals are predatory)
  • charges excessive publication fees to authors
  • lack of peer review/ editorial oversight
  • may mimic the journal name of a legitimate journal (hijacked journals)
  • number of articles published by predatory journals spiked from 53,000 in 2010 to 420,000 in 2014 (8000 active journals)
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3
Q

What was the Bohannon Experiment?

A
  • Dr. John Bohannon, correspondent for Science, submitted a purposefully flawed scientific paper w/ meaningless results to 304 suspect journals
  • responsible peer review process would have promptly rejected
  • half of the journals accepted it
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4
Q

What are 4 Qs to ask about papers you find related to your clinical Q?

A
  1. does the paper have the right study design to answer my clinical Q? (if it wasnt a randomized controlled clinical trial, should it have been?)
  2. which level of evidence does the paper provide?
  3. is the quality of the paper good enough to help me answer my particular question?
  4. is the paper relevant to my clinical Q, my population, or patient?
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5
Q

What are primary research studies?

A
  • case reports
  • case series
  • observational studies (cohort, case-control, cross-sectional)
    diagnostic test validity studies
  • experimental studies
  • clinical trials
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6
Q

What are secondary research studies?

A
  • reviews (narrative reviews, scoping reviews, evidence based practice guidelines, systematic reviews, meta-analysis)
  • economic analyses (partial budgets, decision analysis)
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7
Q

What is a case report?

A
  • descriptive report of unique or interesting case (“story”)
  • may ID a new or unique disease syndrome (“early warning system” - ex: Bo spongiform encephalopathy)
  • cannot make any conclusions regarding efficacy of treatment
  • “expert opinion” on how to handle this specific type of case
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8
Q

What is a case series?

A
  • description of the presentation, Dx, treatment, & outcome of a grp of animals w/ same disease
  • there are no disease-free animals for comparison
  • any differences in treatment or management have not been allocated (these may be due to O’s preferences or individ vet decisions)
  • may allow for more description of manifestations of disease & prognosis
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9
Q

What are surveys/observational studies?

A
  • usually involves obtaining a random sample from a population to obtain an unbiased estimate of the variable of interest
  • important application is often to determine prevalence of disease or if a disease is present @ all
  • available study populations may not always be representative of true target population
  • if all animals in a population are investigated, then the survey is a “census”
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10
Q

Census vs survey?

A

A census includes all of a study population and the measurement is called a parameter (true value of characteristic being measured), while a survey looks at a randomized sample of the study population and its measurement is called a statistic (estimate of parameter)

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11
Q

What are the benefits and downsides to observational studies?

A
  • researcher can study a sp of interest in its natural environment
  • can examine a number of hypotheses that might be difficult to examine in an experimental model
  • can study rare events in large populations
  • harder to control for confounding variables
  • harder to make casual associations
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12
Q

What are the goals of observational studies?

A
  1. measure disease frequency (quantify disease - prevalence/incidence)
  2. assess distribution of a disease (who is getting disease? where is it occurring? when is it occurring? (orienting disease by animal, space, & time))
  3. identify determinants of disease (risk factors; Are exposure & disease linked?)
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13
Q

What are the 2 directions to data gathering?

A
  1. prospective studies
  2. retrospective studies
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14
Q

What is a prospective study?

A
  • looking forward & getting new data after the start of the study
  • clinical trials, experiments, cohort studies must be prospective
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15
Q

what is a retrospective study?

A
  • looking backward & using data that had already been collected
  • case-control studies are retrospective
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16
Q

What are the types of observational studies?

A
  1. cross-sectional studies (longitudinal studies)
  2. case control studies
  3. cohort studies
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17
Q

What is a cross-sectional study?

A
  • sample population is selected randomly or sometimes by convenience WITH NO PRIOR KNOWLEDGE ABOUT EXPOSURE OR DISEASE STATUS
  • sample population is examined @ 1 point in time (usually)
  • each sampling unit is assessed for the factor(s) of interest & the outcome of interest during a “snapshot in time” (best used for chronic diseases or diseases w/ permanent outcomes)
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18
Q

What is a longitudinal study?

A

simply cross-sectional studies that follow the sample population over time to assess for various outcomes (allows us to calculate incidence)

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19
Q

What are the disadvantages of cross-sectional studies?

A
  • weakest observational design (it measures only prevalence, not incidence of disease)
  • the temporal sequence of exposure & effect may be difficult or impossible to determine
  • usually dont know when disease occurred
  • rare events are a problem
  • quickly emerging diseases are difficult to study in this fashion
20
Q

What are the subsets in a population in a cross-sectional study?

A
  • risk factor & disease; risk factor & no disease; no risk factor & disease; and no risk factor & no disease
  • dont know which grp sample belongs to when picking it, but then will ask these Qs
21
Q

What are some sample Qs answered by cross-sectional studies & surveys?

A
  • what is the prevalence of Johnes disease in beef cows in Canada?
  • what biosecurity practices do poultry operations in the Fraser Valley employ?
  • what % of Ca are tested for heartworm in SK?
  • do sheep w/ titres to maedi-visna tend to weigh less?
22
Q

What is a case-control study?

A
  • separate samples of animals/hers w/ & w/o outcome of interest (often a disease) are selected & these 2 grps are then assessed for exposure to the factor of interest & compared (sour gas ex: select farms w/ & w/o repro failure & then assess these herds for exposure to sour gas)
  • easy to perform but prone to more biases
  • usually retrospective in nature
  • good for rare or acute diseases
23
Q

What are the strengths of case-control studies?

A
  • less expensive & time consuming
  • efficient for studying rare diseases
24
Q

What are the limits of case-control studies?

A
  • inappropriate when disease outcome for a specific exposure is not known @ start of study
  • exposure measurements taken after disease occurrence
  • disease status can influence selection of subjects
25
Q

What biases are there in case control studies?

A
  1. sampling bias (bias in selection of cases & controls)
  2. measurement bias (retrospective nature of ID of exposure to risk factors)
    - recall bias
    - avoid using data recorded prior to outcome occurring
    - use of blinding so that observers & study subjects dont know the case-control status & risk factors being studied
26
Q

What are 4 strategies for control selection?

A
  1. hospital/clinic based control
  2. matching
  3. population based sample of controls
  4. 2 or more control grps
27
Q

What are examples of Qs answered by case control studies?

A
  • are Ca w/ Cryptococcus more likely to have spent lots of time outdoors?
  • environmental tobacco smoke & risk of malignant lymphoma in pet cats
  • associations of viral & mycoplasmal antibody titres w/ respiratory disease & weight gain in feedlot calves
28
Q

What is a cohort study?

A
  • 2 samples of subjects are selected on basis of their exposure to some risk factor
  • the subjects are then followed through time for a predetermined period to determine the outcome of interest (the disease)
  • less prone to biases
  • important to ensure validity of exposure, have equal follow-up, & accurate disease diagnosis
  • an observational study design comparing individuals w/ a known risk factor or exposure w/ others w/o the risk factor or exposure
  • looking for a difference in the risk (incidence) of a disease over time
  • best observational design
  • date usually collected prospectively
29
Q

Strengths of a cohort study?

A
  • exposure status determined before disease detection
  • subjects selected before disease detection
  • can study several outcomes for each exposure
30
Q

What are the limitations of a cohort study?

A
  • expensive & time consuming
  • inefficient for rare diseases or diseases w/ long latency
  • loss to follow up can be a major prob
31
Q

Which kinds of Qs are answered by cohort studies?

A
  • are farms next to sour gas wells more likely to see higher rates of reproductive failure in their cow herds?
  • does smoking cause lung cancer?
  • does annual vaccinations of Fe cause fibrosarcoma?
32
Q

What is an experimental study?

A
  • study in which a maneuver is performed on an animal in a controlled & artificial surrounding
  • often disease is artificially created or induced
  • may use lab sp as a model for another sp
  • similar to clinical trials in that 2 or more interventions are usually compared
33
Q

What is a clinical trial?

A
  • interventions ex: drug treatments or surgical techniques, etc. are given to grps of patients & they are followed up to see what happens to them
  • comparison or control grp is used in parallel (parallel arm trial)
  • treatments are randomly allocated
  • patients used are not in a controlled environment (disease occurs naturally, not induced)
34
Q

what is the experimental design of a laboratory experiment?

A
  • comparing 2 or more different interventions
  • under carefully controlled environmental conditions
  • often involve “artificial infectious challenge”
  • may utilize a lab animal sp
35
Q

what is the experimental design of a clinical trial?

A
  • any planned experiment involving human or animal subjects designed to assess the effectiveness of 1 or more treatments or preventative measures
36
Q

What is a RCCT?

A
  • randomized controlled clinical trial
  • controlled means that the experimental subjects receive a new treatment & are compared against other subjects (controls) who receive either a placebo or a standard treatment
  • randomized refers to the method of assignment of subjects to treatment & control grps to minimize “bias”
37
Q

what kind of Qs answered by clinical trials?

A
  • is Nuflor more effective than Micotil in treating Bo resp disease?
  • are omega 3 FAs beneficial in the treatment of pruritis in Ca?
  • which of 2 surgical techniques gives a better rate of recovery?
38
Q

what are the advantages of clinical trials?

A
  • can have a v specific hypothesis to examine in a precise patient grp
  • easier to control confounding variables (eliminates bias if done well)
  • more likely to determine causality (prospective design allows this)
  • can still assess sp in natural environment in field trials
  • allows for meta-analysis @ a later date
39
Q

what are the disadvantages of clinical trials?

A
  • expensive & time consuming (many trials never get done b/c of expense; difficult to perform on rare diseases or events; controlled by lrg pharmaceutical companies, get done in a “cheaper” way by using surrogate end pts)
  • possible to introduce hidden “bias” however this is rare if trial is carried out correctly
40
Q

Compare narrative & opinion reviews:

A
  • traditional review papers
  • aim is to review the literature & give advice
  • if no explicit mention of an organized literature search, then paper is probably an “opinion article”
  • if the literature search is not comprehensive or systematic, then this would be considered a “narrative review”
41
Q

What is a narrative review?

A
  • tend to cover a subset of studies based on availability or author selection
  • can introduce an element of “selection bias”
  • can be informative but not as robust as systemic reviews
42
Q

What is a scoping review?

A
  • used to describe the available literature on a topic
  • “charting or mapping”
  • describes the volume & nature of the existing literature on a topic
  • determine the feasibility of conducting a systematic review
  • research question for a scoping review is often broader in nature
43
Q

What is a systematic review?

A
  • standardized & rigorous methodologies to review all scientific literature for a particular clinical Q (PICO)
  • attempts to minimize bias
  • comprehensive & systematic literature search
  • identify, appraise, & synthesize all relevant studies on a particular topic
  • no combining of data btwn studies
  • formally reports search strategies on all sources including “grey literature”
44
Q

What is grey literature?

A
  • document types produced on all lvls of gov, academics, business, & industry in print & electronic formats that are protected by intellectual property rights, of sufficient quality to be collected & preserved by libraries & institutional repositories, but not controlled by commercial publishers (where publishing is not the primary activity of the producing body)
    ex: conference abstracts, presentations, proceedings, regulatory data, unpublished trial data, gov publications, reports (ex: white papers, working papers, internal documentation), dissertations/theses, patents, & policies & procedures
45
Q

What is a meta-analysis?

A
  • applying stats to a systematic review of all clinical trial data
  • gives a quantitative summary of the info obtained
  • focuses on a COMBINED MEASURE OF TREATMENT EFFECT giving a more precise estimate
  • can be useful for estimating relative importance of different factors affecting the outcome of interest
46
Q

Rank the types of studies from strongest to weakest clinical evidence:

A
  • meta-analysis/systematic review
  • RCCT
  • cohort study
  • case-control study
  • cross-sectional study
  • case series
  • case report

Evidence Based Medicine (8 decks)

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