5 - Variability and Standard Scores

# 5 - Variability and Standard Scores - Chapter 6:...

This preview shows pages 1–9. Sign up to view the full content.

Chapter 6: Variability and Standard (z) Scores Measure of Variability Single summary figure describing the spread of observations in the distribution Means different things in different settings Imprecision in a measure Individual differences “Error” in a study

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
Measures of variability are quantitative indices of the extent to which scores in the distribution are similar or dissimilar Not Information about an individual score Shape of the distribution
How would you describe the variability (spread) of scores?

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
Variability measures include Range Semi-Interquartile Range Average Absolute Deviation Variance Standard Deviation
Range Range Difference between the lowest and highest score in the distribution A distance (like other variability measures) Central tendency is location For grouped data, use highest and lowest possible raw scores

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
Range Only two scores affect the value Highly unstable Tends to increase with sample size Little use in inferential statistics
Semi-Interquartile Range Semi-Interquartile Range (Q) Half the distance between the first and third quartiles (i.e., P 25 and P 75 ) Quartile Points : The three score points that divide distribution into four parts with = number of frequencies (2nd quartile = P 50 ) Q P P = - 75 25 2

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
Semi-Interquartile Range Could also think of Q as mean distance between the median (P50) and the other two quartiles (P25, P75)
This is the end of the preview. Sign up to access the rest of the document.

## This note was uploaded on 04/17/2008 for the course PSY 201 taught by Professor Arthur during the Spring '08 term at Purdue University-West Lafayette.

### Page1 / 32

5 - Variability and Standard Scores - Chapter 6:...

This preview shows document pages 1 - 9. Sign up to view the full document.

View Full Document
Ask a homework question - tutors are online