Descriptive statistics

Descriptive statistics

1. Measures of Central Tendancy

   • Mean - the mean is used with interval data. It is calculated by adding all the scores together in each condition and then dividing the number of scores. This is a useful statistic as it takes all of the scores into account, and therefore a very sensitive measure.
   • Median - the median is used with ordinal data. It is calculated by finding the mid-point in an ordered list. The median is calculated by placing all the values of one condition in order and finding the mid-point. This is a more useful measure that the mean when there are extreme values.
   • Mode - the mode is the most common value in a set of values. it is used with nominal data. This is probably the least valuable measure of central tendancy as sometimes there may be more than one mode or no mode at all. However, it is useful when using categories.

2. Measures of Dispersion

   • Variance - this tells use more than the range. Instead of looking at just the highest and lowest figures, it considers the difference between each data point and the mean. The difference is called the deviation from the mean.
   • Range - To calculate the range, you only have to simply note the differences between the scores, or by doing do and then adding one.
   • Standard Deviation - This is the most sensitive measure of dispersion, It overcomes a particular problem with the variance, which is that the final answer is a squared number. The standard deviation includes an additional end step; simply to calculate a square root. This returns a figure to the same units as the mean and makes it easier to make direct judgements about the data set. Although it is a very sensitive measure, it can take time to calculate.