Summary Measures in Statisitics

  • Abigail B. Shoben

Learning Objectives

  1. 1.
    Three types of variables are commonly used in clinical research studies:
    1. (a)

      Continuous – can take on an infinite number of possible values

    2. (b)

      Binary – can take on only two possible values

    3. (c)

      Categorical – can take on only a few possible values

  2. 2.

    A histogram plots the observed values of a variable on the X-axis versus the relative frequency of these values on the Y-axis.

  3. 3.

    The arithmetic mean describes the middle of the data for symmetric distributions, including data from normal-appearing distributions.

  4. 4.

    The median refers to the value within a distribution for which exactly half of the data fall above this value and half fall below it.

  5. 5.

    Disagreement between mean and median values suggests that a distribution is not normally distributed.

  6. 6.

    A continuous variable may be divided into 3, 4, or 5 equally sized groups called tertiles, quartiles, and quintiles, respectively.

  7. 7.

    The interquartile range is defined as the 25th and 75th quantiles of a distribution.

  8. 8.

    Some techniques to describe the joint distribution between two variables include tabulation across categories, scatter plots, correlation, and quantile-continuous plots.

  9. 9.
    Correlation coefficients are interpreted as:
    1. (a)

      +1 indicates perfect positive agreement between two variables

    2. (b)

      0 indicates no agreement between two variables

    3. (c)

      –1 indicates perfect negative agreement between two variables



Chronic Kidney Disease Systolic Blood Pressure Binary Variable Joint Distribution Summary Measure 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Copyright information

© Springer Science+Business Media, LLC 2009

Authors and Affiliations

  • Abigail B. Shoben
    • 1
  1. 1.Department of BiostatisticsUniversity of WashingtonSeattleUSA

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