Definitions of Abnormality
Ever wondered how psychologists decide what's "normal" versus "abnormal"? It's trickier than you might think, and there are four main approaches they use.
Statistical infrequency is the simplest approach - if very few people do something, it's considered abnormal. For instance, having an IQ below 70 affects only about 2% of the population, so it's classified as abnormal and can lead to a diagnosis of intellectual developmental disorder.
This method works well in real-life diagnosis and assessment. The Beck Depression Inventory, for example, uses statistical cut-offs where only 5% of people score high enough to indicate severe depression. However, it has a major flaw: it can't tell the difference between rare but desirable traits (like having an IQ over 130) and genuinely problematic behaviours.
Key Point: Not all statistically rare behaviours are undesirable - some are actually brilliant!











