Inferential Statistics

When psychologists wish to make inferences about collected data in order to estimate the likelihood that the data collected occurred due to chance or to draw conclusions about a larger population from which the sample was collected

• More powerful and robust methods of analysis 
• More accurate estimates of probabilities are collected, making type 1 and 2 errors less likely to occur

• The data must be precise, interval level of measurement 
• Scores must be drawn from a normal distribution of the population with few scores at both ends and more in the middle 
• The variability of the two sets of the scores must be similar

• The mean, median and mode are compared
• If the data is of a normal distribution, these figures should be similar

The standard deviation²  

• The range
• The standard deviation
• The variance 
• Dot plot or box plots

• The data must be nominal or ordinal 
• Results must be of a skewed distribution
• There must be a wide variance in scores between two sets

• Am I looking for a difference between scores or a correlation?
• What type of design have I used?
• What level of measurement have I used?