descriptive statistics

• descriptive statistics 


  l

  
• measures of central tendency 


  • A measurement of data that indicates where the middle of the information lies e.g. mean, median or mode
• mean 


  • Measure of central tendency calculated by adding all the scores in a set of data together and dividing by the total number of scores
• evaluation of the mean


  • Most informative as it takes every score into account
  • Any data that is greatly larger or smaller (extreme values) in comparison with the other pieces of data can distort the mean
  • Sometimes the mean doesn’t make sense in terms of what the data is about
• median

  • Measure of central tendency calculated by arranging scores in a set of data from lowest to highest and finding the middle score
• evaluation of the median


  • It is less affected by extreme scores
  • It is not suited to being used with small sets of data, especially if it contains widely varying scores
• mode 


  • the most frequently occurring score in a set of data. When there is more than one number that appears the most frequently, we call this bimodal.
• evaluation of the mode 


  • Is not affected by extreme scores
  • Gives a good idea of how often something is occurring e.g. what mobile phone is selling the most
  • A set of data may not have a most frequent score
• range 


  The distance between the lowest and the highest value in a set of scores. It is also a measure of dispersion which involves subtracting the lowest score from the highest score in a set of data

  • Easy to calculate
  • Only using two scores in the data set and ignoring the rest
  • The extreme scores could distort the range
• standard deviation


  •  A measure of the average spread of scores around the mean. The greater the standard deviation the more spread out the scores are.
  • To work out standard deviation: 1. Work out the Mean (the simple average of the numbers), 2. Then for each number subtract the Mean and square the result, 3. Then work out the mean of those squared differences, 4. Take the square root of that and we are done
• standard deviation eval


  • SD is the most sensitive measure of dispersion as it is derived by using every score in the data set 
  • Is not very distorted by extreme scores.
  • The SD is closely related to the mean and is the best measure of dispersion to use when the mean is being used as the measure of central tendency
  • Takes a long period of time to calculate
  • Assumes a normal distribution