Data Preparation and Analysis – Descriptive Statistics

Descriptive statistics describe the data but do not draw conclusions about the data.  Descriptive statistics are normally applied to a single variable at a time.  They can tell the researcher the central tendency of the variable, meaning the average score of a participant on a given study measure.  The researcher can also determine the distribution of scores on a given study measure, or the range in which scores appear.  Finally, descriptive statistics can be used to tell the researcher the frequency with which certain responses or scores arise on a given study measure.  For example, in our imaginary study about the effectiveness of corrective lenses on economic productivity, the researcher might observe that the average dollars-per-week (DPW) of a person with corrected vision is $500, whereas the average DPW for a person without corrected vision is $450.  A good researcher will know that this is not enough information to conclude that vision correction has an effect on economic productivity. Inferential statistics are necessary to draw conclusions of this kind.  Descriptive statistics might also tell the researcher that the distribution of DPW is $351-$640 for the whole sample, and that the average DPW is $445 for the sample.

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