How to Read Scientific Journal Articles

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How to Read Scientific Journal Articles
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Major article sections

• Abstract -- brief summary of entire article
• Introduction -- includes literature review
  states why the research is relevant.
• Methods -- identifies how patients were selected,
  what study procedures entailed, and statistical
  methods used.
• Results -- presents objective results
• Discussion -- interprets results states study
  strengths/weaknesses identifies future work

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What population(s)?

• The study eligibility criteria define the
  characteristics of the patients studied, and
  therefore the population(s) to which the results
  can be extended.
• The baseline characteristics define the
  characteristics of the patients studied, and
  therefore the population(s) to which the results
  can be extended. (Often, Table I.)

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Identification of groups

• Typically, one group is considered a control
  group, while other groups are considered new
  treatment groups.
• The groups should be similar, on average, except
  with respect to the primary treatment(s) of
  interest. (Often, Table I.)
• Ideally, groups will be created by randomly
  assigning individuals to groups.

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With respect to what are the groups being
compared?

• The main variables by which the groups are
  compared are called the primary outcome measures.
• A good study is designed with the primary outcome
  measures in mind.
• The less important variables by which the groups
  are compared are called the secondary outcome
  measures.

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How are outcome measures be analyzed
statistically?

• The type of data and how the study was designed
  determine the appropriate analysis methods.
• Categorical (binary) data are often summarized as
  percentages, but also odds ratios and relative
  risks.
• Numerical (measurement) data are often summarized
  as means, but also medians.

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Presentation of results

• Statistical results can be presented in words or
  in a table.
• If a summary measure, like a percentage or a
  mean, is reported without a P-value or a
  confidence interval, the result only applies to
  the sample of patients in the study.

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Presentation of P-values

• In a table, P-values are usually indicated by a
  footnote.
• In writing, P-values are usually indicated in
  parentheses after the conclusion of a hypothesis
  test is stated.
• It is the readers job to infer the null and
  alternative hypotheses of the hypothesis test.

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Presentation of confidence intervals

• Confidence intervals for a mean are typically
  presented in one of three ways.
• Sample mean SD, (standard deviation)
• Sample mean SE (standard error)
• The lower and upper limits of the interval
• If Sample mean SD, the 95 margin of error is
  2(SDsqrt(n))
• If Sample mean SE, the 95 margin of error is
  2SE.

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Presentation of confidence intervals

• It is the readers job to know what value is
  relevant to the confidence interval
• If a confidence interval for a difference in two
  means or a confidence interval for a difference
  in two proportions, then is 0 in the interval?
• If a confidence interval for a relative risk, or
  a confidence interval for an odds ratio, then is
  1 in the interval?
• And so on ...

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Evaluation of the strengths/weaknesses of the
study

• Is there a control group?
• Is the study a randomized experiment or an
  observational study?
• Were the patients selected and assigned to their
  treatments in an unbiased manner?
• Were the patients and physicians blinded to
  treatment assignment?

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Evaluation of the strengths/weaknesses of the
study

• Was the sample large enough to get useful
  statistical results?
• If the sample was really large, were confidence
  intervals created to show that a rejection of the
  null hypothesis is actually meaningful?
• Are the conclusions of the study overstated?
• Do the authors point out future necessary
  research?