distributions

• Histogram


  Displays the frequency of continuous numerical data. The frequency is placed on the Y-axis, and the continuous variable (e.g. test scores).
• Normal distribution


  When recording the frequency distribution of certain variables (e.g. IQ), the graph forms a naturally occurring symmetrical bell-shaped distribution curve. More participants are in the middle, with few participants on either side.

  MEAN-MEDIAN-MODE
• Characteristics of normal distributions


  Measures of central tendency:

  Mode: Highest/midpoint. The highest point in a histogram is the most frequent score.

  Median: Highest/midpoint. An equal number of scores on either side (symmetrical).

  Mean: Highest/midpoint. An equal number of outlier scores on either side.
• Characteristics of normal distributions


  Standard deviations:

  When data is normally distributed, 68% of scores in the data set fall within one standard deviation of the mean, and 95% of scores are within two standard deviations of the mean.
• Skewed distribution


  The distribution of scores is asymmetric. Most of the scores are on one side, with long skews (tails) on the opposite side to the majority of scores.
• Positive skew 


  More scores at the lower end of the graph, outliers at the higher end.

  MODE-MEDIAN-MEAN

  
• Negative skew


  More scores at the higher end of the graph, outliers at the lower end.

  MEAN-MEDIAN-MODE

  
• Characteristics of skewed distributions - measures of central tendency


  Mode: As the mode is the most frequent score, it remains at the highest point.

  Median: At the point where 50% of the graph is either side (between mode and mean).

  Mean: Shifted towards the outlier scores in the long tail (skew).