Descriptive Statistics

• Descriptive Statistics definition


  Methods that describe the patterns found in a set of data
• Measures of central tendency 


  • Averages
  • Indicate the most typical values in a set of results
• How is the mean calculated


  Add up all the values and divide it by the total number of scores 
• Advantage of means 


  • Most sensitive as it includes all the values so is more representative
• Disadvantage of mean 


  • Easily distorted by extreme values
  • Unrealistically precise e.g. 2.4 children
• How to calculate the median 


  Find the middle value of a data set
• Advantage of median 


  • Extreme scores do not affect it
  • It is quick and easy to calculate
• Disadvantage of median 


  • Less sensitive as not all the scores are included in the final calculation
• How to calculate the mode


  Find the most frequent value
• Advantage of mode

  • Easy to calculate
  • Shows common value
  • Result is from the data set
• Disadvantage of mode

  • Crude measures
  • Not useful if there are many modes
• What is measures of dispersion 


  How spread out the data is
• What is the range


  It takes the lowest value away from the highest value and then adds 1

  You add 1 to account for the .5 scores that are often rounded
• Advantage of range 


  Easy and quick to calculate
• Disadvnatage of range 


  Only takes into account the 2 extreme variables - unrepresentative

  Not sensitive so it is less accurate
• How to overcome disadvantage of range 


  Interquartile range

  1. Find the median of all the values
  2. Median of the lower half = lower quartile and median of the upper half = upper quartile
  3. IQR = Q3-Q1
• Measures of central tendency and dispersion can be used together to give us more information about our sample
• What is standard deviation 


  Measures the 'spread' or dispersion of values around the mean value

  The larger the number the greater the spread

  When the SD is small, it means that there is less variation in the data and the values are closer to the mean

  When the SD is large it means that there is a lot of variation

  If SD is 0 all of the data set values are the mean
• Advantage of standard deviation 


  It is sensitive as it uses all the values in the data set, so is more accurate and valid
• Disadvantage of standard deviation 


  Hard to calculate
• Key words of descriptive statistics 


  • Variation
  • Spread
  • Clustered
  • Similar