Norm groups & SEMean

In this unit, you will recap the main measures of central tendency and dispersion, such as the mean, median, mode, range, and standard deviation, and understand their limitations in psychometrics. You will learn about Z scores and other standard scoring systems, as well as the importance of norm groups. The unit also introduces the concept of the standard error of the mean and explains how it relates to confidence in how well a sample mean represents the wider population. Different methods of sampling for norm groups are discussed, highlighting their impact on accuracy and representativeness.

After this talk, you will:

• Understand the concepts of norm groups and standard error of the mean.

• Be able to recall and explain the measures of central tendency: mean, median, and mode.

• Know why measures of central tendency alone are not always useful in psychometrics.

• Understand the importance of measures of spread, such as range and standard deviation.

• Be able to explain what standard deviation is and how it is calculated.

• Understand the concept of Z scores and how they relate to standard deviation.

• Know the different standard score systems (Z scores, T scores, Stanines, percentiles) and their properties.

• Be able to recall the mean and standard deviation values for common scoring systems.

• Understand how to convert between different standard score systems.

• Learn what standard error of the mean (SE mean) is and why it matters.

• Be able to calculate and interpret standard error of the mean using the correct formula.

• Recognise how confidence levels (68%, 96%, 99%) relate to standard error of the mean.

• Know why sample size affects the standard error of the mean.

• Understand the difference between incidental, stratified, and random sampling for norm groups.

• Appreciate why truly random sampling is rarely achieved in psychometric test norm groups.