AO1 - Statistical Infrequency

• This is a mathematical method for defining abnormality.
• Based on the idea that abnormality should be infrequent so if it occurs rarely then it is abnormal.
• The mathematical element of the definition is about the idea that human attributes fall into a normal distribution within the population.
• Most human characteristics are spread in a normal way across the general population.
• The majority of people fall into the middle of a normal distribution graph with a minority being at either extreme.
• Most people fall into the ‘normal’ band, whereas those with mental health issues at the extremes.
• Mental health issues are based on statistically rare cases.
• In a normal distribution most scores are around the mean (average), but some are at either extreme.
• The extreme scores on a normal distribution graph are measured using the standard deviation.
• The standard deviation (sd) tells us the spread of scores away from the mean. A greater sd means there is more variation in the scores.
• If we plot IQ on a normal distribution, most people will be around the average (mean) with some at either extreme (above or below).