descriptive statistics

• descriptive statistics are the use of tables, graphs and summary statistics to analyse data
• measures of central tendency refer to any measure which calculates an average value within a set of data
• mean


  a measure of central tendency calculated by adding all the scores in a set of data together and dividing by the total number of scores.
• A strength of the use of mean is that it makes use of all values and is good for interval data
• A limitation of mean is that it is influenced by outlying data so it can be unrepresentative
• median


  a measure of central tendency where data is arranged from lowest to highest and identifying the middle score
• a strength of the use of median is that it is not affected by extreme scores and it good for ordinal data
• mode


  a measure of central tendency which is the most frequently occurring score in a set of data
• a strength of mode is that it is useful for nominal data.
• a limitation for mode is that it is not useful when there are several modes.
• measures of dispersion


  any measure that calculates the variation in a set of data
• range


  subtracting the lowest score from the highest score in a set of data
• a strength of range is that it is easy to calculate
• a limitation of the range is that it is affected by extreme values and does not use all data
• standard deviation


  the average spread of scores around the mean. a measure used to identify the amount of variation or dispersion of a set of data values
• a strength of standard deviation is its a precise measure where all data values are taken into account
• a limitation of standard deviation is that it is difficult to calculated and is affected by extreme results.
• there are various ways of representing data:

  • summarising data in a table
  • bar chart
  • histogram
  • line graph
  • scattergrams
• bar chart


  a graph that shows data in the form of categories that the researcher wishes to compare. The bars do not touch each other. The frequency is plotted on the y-axis and the categories are plotted on the x-axis
• a strength of bar charts is that it is a way of representing data that allows for differences in data to be seen more clearly
• histograms


  a graph that is used for continuous data. there should be no space between the bars because the data is continuous
• line graphs


  represents continuous data where points are connected by lines to show the change of values.
• scattergrams


  used to show associations between covariables
• normal distribution


  a symmetrical arrangement of data which forms a bell shaped pattern where the mean, median and mode all fall in the centre at the highest peak
• skewed distribution


  an arrangement of data that is not symmetrical as data is clustered to one end of the distribution
• positive skewed data


  where most of the data is concentrated on the right
• negative skewed data


  most of the data is concentrated on the left