Chapter 5 & 6 - Z-Scores and Probability and Normal Distribution

2 purposes of Z-Scores

• see the position of a score within a distribution

• to standardize an entire distribution

  • so scores can be compared to other measures

    • ex; helping behaviour rated 1-10 and 1-100 can be compared if changed to Z-Scores

Standardized Distribution

• when every score is converted to a z-score

• the shape of your distribution and the position of scores in the distribution remains the same (just on a new scale)

  • more like “re-lablling” on a new standardized scale

• mean is always 0

• standard deviation is always 1

p-value

• probability value

• tells you if you have a “statistically significant” difference

• so we want a lower value (lower probability that your effect is a “mistake”)

Inferential Statistics

• take smaller sample and infer the probability of this in a population

Probability

• take a big number (population) and guess probability of this in smaller group (sample)

The Unit Normal Table

• tells us the proportion of the normal distribution that corresponds to each z-score