Basic Science - Statistics - Research and Journals

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  1. Level of evidence?
    The Oxford CEBM Levels of Evidence

    • 1a: Systematic reviews (with homogeneity) of randomized controlled trials
    • 1b: Individual randomized controlled trials (with narrow confidence interval)
    • 1c: All or none randomized controlled trials

    • 2a: Systematic reviews (with homogeneity) of cohort studies
    • 2b: Individual cohort study or low quality randomized controlled trials (e.g. <80% follow-up)
    • 2c: "Outcomes" Research; ecological studies

    • 3a: Systematic review (with homogeneity) of case-control studies
    • 3b: Individual case-control study

    4: Case series (and poor quality cohort and case-control studies)

    5: Expert opinion without explicit critical appraisal, or based on physiology, bench research or "first principles"
  2. What is Grades of recommendation?
    A - Strong recommendation to perform this procedure. There is good evidence to support its clinical effects.

    B Fair recommendation to perform this procedure. There is fair evidence to support its clinical effects.

    C1 - Poor recommendation to perform this procedure. The existing evidence is poor, but there is a possibility of favorable effects.

    C2 -  Recommendation undetermined. The existing evidence is poor or conflicting, and does notallow for making a clear recommendation.

    D -  Recommendation not to perform this procedure. There is evidence to deny its usefulness, or to show its adverse effects.
  3. Phases of Clinical trial?
    Preclinical - Testing of drug in non-human subjects, to gather  efficacy,  toxicity  and pharmacokinetic information

    • Phase I studies
    • - assess the safety of a drug or device.
    • - Sample size - 10-20 healthy volunteers. 
    • - Unexpected side effect may occur. 

    • Phase II studies
    • - test the efficacy of a drug or device.
    • - involves up to several hundred patients
    • - Most phase II studies are randomized trials where one group of patients receives the experimental drug, while a second "control" group receives a standard treatment or placebo.
    • - Most research project fail in phase II due to product not being as effective as anticipated. 

    • Phase III studies
    • - involve randomized and blind testing in several hundred to several thousand patients.
    • - can last several years
    • - provides a more thorough understanding of the effectiveness of the drug or device, the benefits and the range of possible adverse reactions
    • - Once Phase III is complete, a pharmaceutical company can request FDA approval for marketing the drug.
    • - Likelihood to detect rare side effects increases with number of people involved. 


    • Phase IV studies
    • - Post Marketing study
    • - Objectives at this stage:
    • - (1) to compare a drug with other drugs already in the market;
    • - (2) to monitor a drug's long-term effectiveness and impact on a patient's quality of life; and
    • - (3) to determine the cost-effectiveness of a drug therapy relative to other traditional and new therapies.
  4. What is Impact Factor?
    In any given year, the impact factor of a journal is the number of citations received in that year by articles published in that journal during the two preceding years, divided by the total number of articles published in that journal during the two preceding years. 

  5. Highest impact factor journals
    • Category "General & Internal Medicine
    • The New England Journal of Medicine- 59.558 (2015) - the only journal in the category with an impact factor of more than 50
    • The Lancet - 45.217
    • Journal of American Medical Association (JAMA) - 35.289

    • In Surgery 
    • British Journal of Surgery - 5.542 (2014)
    • Annals of Surgery - 4.5
  6. What is volume and Issue in Journal?
    In a quarterly, periodical, newsletter and literary journals, the volume number refers to the number of years a journal has been in publication.

    Issue number refers to the number of individual publications during the year.

    While most journals use volume numbers, many of them do not use issue numbers, and those journals simply paginate their publications consecutively throughout the year. For example, when a journal's first publication of the year ends on page 124, the second publication of the year begins on page 125. When the volume is complete, it is paginated in the manner of a book
  7. Classification of RCT?
    • By study design
    • Parallel-group – each participant is randomly assigned to a group, and all the participants in the group receive (or do not receive) an intervention.
    • Crossover – over time, each participant receives (or does not receive) an intervention in a random sequence
    • Cluster – pre-existing groups of participants (e.g., villages, schools) are randomly selected to receive (or not receive) an intervention.
    • Factorial – each participant is randomly assigned to a group that receives a particular combination of interventions or non-interventions (e.g., group 1 receives vitamin X and vitamin Y, group 2 receives vitamin X and placebo Y, group 3 receives placebo X and vitamin Y, and group 4 receives placebo X and placebo Y).


    • By outcome of interest (efficacy vs. effectiveness) -
    • Explanatory - test efficacy in a research setting with highly selected participants and under highly controlled conditions.
    • Pragmatic - test effectiveness in everyday practice with relatively unselected participants and under flexible conditions; in this way, pragmatic RCTs can "inform decisions about practice."


    • By hypothesis (superiority vs. noninferiority vs. equivalence)
    • Most RCTs are superiority trials, in which one intervention is hypothesized to be superior to another in a statistically significant way.
    • Some RCTs are noninferiority trials "to determine whether a new treatment is no worse than a reference treatment
    • Other RCTs are equivalence trials in which the hypothesis is that two interventions are indistinguishable from each other.

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Basic Science - Statistics - Research and Journals
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2017-06-19 11:40:41
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