Normal Distributions (OCR GCSE Psychology): Revision Note

The characteristics of a normal distribution

• In psychology, distribution refers to how data is spread around the mean for a particular sample or population

  • Researchers are interested in how much individual scores vary from the mean — whether most scores cluster closely around it, spread out evenly, or are skewed to one side

• A normal distribution is a symmetrical spread of data around the mean, with most scores close to the average

• When plotted on a graph, it forms a distinctive bell-shaped curve, with a peak in the middle representing the mean value

• This curve is known as the ‘bell curve’ because when a line is drawn around the histogram bars, it resembles the shape of a bell.

Interpreting a normal distribution

• In a perfect normal distribution, the mean, median, and mode all appear at the peak of the curve, meaning they have the same (or very similar) value

  • Scores to the left of the peak represent people scoring below the mean

  • Scores to the right represent people scoring above the mean

• The tails at both ends of the curve never touch the x-axis, as it is assumed that extreme scores could exist beyond those measured (e.g. very low or very high values)

• Normal distributions are common in naturally occurring characteristics such as:

  • height

  • shoe size

  • IQ (intelligence quotient)