Bit More About Central Tendency

Although some use case studies, naturalistic observation, and single subject studies (N=1), most research is group based. Usually, there are lots of numbers from lots of subject, all waiting to be crunched. So the first thing to do after conducting a study is to organize its data. A data matrix is a table of data. Each row holds the scores of a single subject. Each column is a different variable. The simplest data matrix has two columns: one for the ID number and one for the score. And it would have as many rows as subjects in the study.

After forming a data matrix the next step is usually to plot the data. Each variable is plotted separately: a graph for each factor being measured. Sometimes the variables are summarized in histograms (vertical bar graphs). Often the graphs are frequency distributions: overviews of the raw data. Each score is listed from lowest to highest (left to right). If more than one person has the same score, the graph points are stacked vertically.

So, if no one has the same score, the frequency distribution would look like a straight horizontal line. If everyone had the same score, it would be represented by a vertical line. If there is some variability in scores but several people with the same score, the distribution will have both width and height. The typical frequency distribution varies from left to right but most scores are in the middle. The result is a graph that looks like a mountain…or a dome…or the bottom of a bell. If frequency distributions are not “normal bell-shaped curves,” they might be positively skewed, negatively skewed, or bimodal.

NOW YOU CHOOSE:
   Day 2: Central Tendency
   A Bit More About Central Tendency
   Even More About Central Tendency
   More Examples
      More Mean Examples
      More Median Examples
      Median Is Middle Of Distribution
      More Mode Examples
   Impact of Outlying Scores
      On The Mean
      On The Median
      On The Mode
   How To Calculate Central Tendency
      Calculating The Mean
      Calculating The Median
      When There’s No Middle-Most Score
      Calculating The Mode
   Formulas For Central Tendency
   Basic Facts About Central Tendency
   Vocabulary
   Quiz 2
   Summary