Distribution of data and histograms

• Normal

  • bell shaped curve
  • Mean, median and mode should be aligned around midpoint
  • Tail ends shouldn’t meet the horizontal axis
• • a normal distribution means that most of the examples in in a set of data are close to the average while relatively few examples tend to one extreme or the other
• • Standard deviation calculates the distance of a score from its group mean
• Skewed

  • data that is multimodal is not normally distributed 
  • When a mean median and mode are not similar distribution will be skewed 
  • Data distributions can be skewed due to extreme outliers
• Use feet method to remember positive vs negative skew 

  • Left foot negative
  • Right foot positive 

  
• In a normal the mean=median=mode they are all in the middle of the bell curve diagram 
• In a skew diagram highest point in mode, middle is median and lowest in mean

  • for positive this means mode< median < mean
  • For negative mean<median<mode
• What curve is this : negative skew

  
• What curve is this : Positive skew

  
• What curve is this : Normal distribution

  
• • Histograms show frequencies using columns.
• • Histograms should be used to display data distributions of continuous data and there should be no gaps between the bars.
• Continuous Data: Can Take Any Value (within a range) e.g. Height, Weight, IQ score, Histograms display only continuous data.
• Class width formula:

  Frequency density = frequency % class width