1. Descriptive Statistics  Measure of central tendency  Gives a typical value for the data set  Tells you where the middle of the data set is  Measure of dispersion  Indicates how the data are spread out  Tells you what the rest of the data are doing www.psychlotron.org.uk

2. Descriptive Statistics  The aim of descriptive statistics is to give an accurate summary of the data  The wrong choice of statistic gives a distorted picture of the data  This can lead to the wrong conclusions being drawn from the data  Each measure of CT and D has its advantages and disadvantages www.psychlotron.org.uk

3. Measures of Central Tendency  The mean  Adv: it uses all the values in the set, so is most sensitive to variations in the data  Dis: it can be artificially raised or lowered by an extreme value, or by skewed data  Use it when the data are normally distributed, unskewed and there are no outliers www.psychlotron.org.uk

4. Measures of Central Tendency  The median  Adv: it is based on the order of the data, not their actual values, so not distorted by extreme values  Dis: however, this makes it less sensitive to variations in the data  Use it when you can’t use the mean because of skew, outliers etc. www.psychlotron.org.uk

5. Measures of Central Tendency  The mode  Adv: it’s the only measure suitable for summarising category/frequency data  Dis: for many data sets there is no modal value, or their may be several  Use when dealing with frequency data, and/or where there is a clear modal value in the set www.psychlotron.org.uk