Distribution of data

• Normal distribution curve

  -shows that the data set is normally distributed around the mean

  -mean, median + mode are together in the centre

  -50% of scores to the left + 50% of scores to the right

  
• Analysis of a normal distribution curve


  68% of scores fall 1 SD from the mean

  95% of scores fall 2 SD from the mean

  99.7% of scores fall 3 SD from the mean

  
• Example Qs


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• Skewed distributions


  -spread of data is skewed + is more on one side of the curve than the other

  -mean, mode + median will be at different points

  
• Positive skew


  curve is more to the left due to majority low scores and the mean is skewed by a few extremely high scores which pulls mean to the right
• Negative skew


  curve is to the right due to majority high scores and the mean is being skewed by a few extremely low scores which pulls mean to the left
• How SD affects distribution curve


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• What would the difference in SD mean for a study on test scores


  if the SD for test scores are high then each person scored inconsistently in relation to the mean. if the SD for test scores is low then each person scored consistently in relation to the mean