Deviation from Statistical Norms
Put simply, if few people in a given population behave like you then you’re abnormal! This appears to have ‘face validity’ in that it appears to make obvious sense at first sight. However when we dig a little deeper it fails miserably.
Let’s start with a physiological example. If we take 5’ 9’’ as the average height of an adult male in the UK, surely it is safe to assume that 4’ or 7’ is abnormal since a tiny percentage of the population fall into these categories.
However, when we consider psychological characteristics things are not so clear cut. Let’s consider IQ (intelligence quotient). Within a population this is normally distributed. When plotted on a graph it assumes the familiar ‘bell-shaped’ curve.
Put simply, if few people in a given population behave like you then you’re abnormal! This appears to have ‘face validity’ in that it appears to make obvious sense at first sight. However when we dig a little deeper it fails miserably.
Let’s start with a physiological example. If we take 5’ 9’’ as the average height of an adult male in the UK, surely it is safe to assume that 4’ or 7’ is abnormal since a tiny percentage of the population fall into these categories.
However, when we consider psychological characteristics things are not so clear cut. Let’s consider IQ (intelligence quotient). Within a population this is normally distributed. When plotted on a graph it assumes the familiar ‘bell-shaped’ curve.
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The average IQ in the UK is maintained at 100 with a standard deviation of 15. For the innumerate amongst you that means in simple English that 67% of the population have an IQ of between 85 and 115 (one standard deviation below the average and one standard deviation above the average). By the time we reach 3 standard deviations below the norm, an IQ of 55 (3 x 15 =45 and 100 -45 =55), are you still with me, we are talking less than 1% of the population. Surely we can consider these to be abnormal since they are so rare. |
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Evaluation
Where do we draw the line? If we assume that an IQ of 100 is normal and one of 70 is abnormal at what point between do we cease to be normal, 73, 72, 71 …? Our decision has to be arbitrary and will probably be on mathematical grounds such as standard deviation. Depression is notoriously unreliable in its diagnosis. Part of this involves characteristics such as ‘difficulty sleeping.’ How much time less spent asleep would be classed as ‘abnormal?’ Who decides?
Is the behaviour desirable? We tend to associate abnormality with undesirable or unwanted behaviour, but statistically rare will encompass desirable characteristics such as genius, very low levels of stress and anxiety etc.
Rare or not reported? It is thought that some disorders appear rare in a culture simply because they are not reported. Cohen (1988) believes that few mental illnesses are reported in India because mental illness is seen as a curse so sufferers are looked down upon. Similarly, Rack (1982) believes that depression is far more prevalent in Asian culture than the figures would suggest. Asians tend to report physical illness but mental illness is dealt with within the family to avoid stigmatisation.
One final point to ponder. In 1994 Kessler et al reported that 48% of Americans had suffered a period of mental illness. Using the statistical infrequency definition it can only be a matter of time before that figure reaches and exceeds 50% meaning that those without mental illness are in a minority… and presumably as a result abnormal!
Where do we draw the line? If we assume that an IQ of 100 is normal and one of 70 is abnormal at what point between do we cease to be normal, 73, 72, 71 …? Our decision has to be arbitrary and will probably be on mathematical grounds such as standard deviation. Depression is notoriously unreliable in its diagnosis. Part of this involves characteristics such as ‘difficulty sleeping.’ How much time less spent asleep would be classed as ‘abnormal?’ Who decides?
Is the behaviour desirable? We tend to associate abnormality with undesirable or unwanted behaviour, but statistically rare will encompass desirable characteristics such as genius, very low levels of stress and anxiety etc.
Rare or not reported? It is thought that some disorders appear rare in a culture simply because they are not reported. Cohen (1988) believes that few mental illnesses are reported in India because mental illness is seen as a curse so sufferers are looked down upon. Similarly, Rack (1982) believes that depression is far more prevalent in Asian culture than the figures would suggest. Asians tend to report physical illness but mental illness is dealt with within the family to avoid stigmatisation.
One final point to ponder. In 1994 Kessler et al reported that 48% of Americans had suffered a period of mental illness. Using the statistical infrequency definition it can only be a matter of time before that figure reaches and exceeds 50% meaning that those without mental illness are in a minority… and presumably as a result abnormal!