Z-scores

Research Methods and Data Analysis

when are values classed as extreme?

when they are greater than 1.96 or less than -1.96

why Z-scores?

they allow comparison between variables that are measured in separate units

what do Z-scores tell us?

how many Sd units a score is from the mean

what does a positive Z-score indicate?

that the observation is greater than the mean

what does a negative Z-score indicate?

that the observation is less than the mean

what does the absolute value tell us?

Z-score magnitude: how far the score is from the mean

formula for calculating the Z-score?

𝑋−𝜇 / 𝜎
( score- mean of scores / SD )

to find %: largest percentage- smallest percentage

Z-scores and confidence intervals (probable limits)?

95% CI: ± 1.96

99% CI: ± 2.58

formula: μ ± ( z critical X σ )