W3 - Descriptive Statistics Flashcards
Define nominal scale
Subjects grouped into mutually exclusive categories.
Examples of nominal scale
Eye colour
Year of birth
Define ordinal scales
Ranks subjects/scores in order.
Doesn’t indicate how much better 1 score is to another.
Example of ordinal scales
University rankings
Define interval scales
Equal units or intervals between data points on a scale, but there’s no zero point.
Example of interval scales
Temperature
Define ratio scales
Equal units of measurement
Established 0 point.
Example of ratio scales
Mass
Length
Height
What are measures of central tendency used for?
To summarise or provide meaning to a whole dataset
To provide a ‘central’ value
What doesn’t central tendency show?
Distribution of scores
What is the SD?
Avg distance away from mean
What allows you to summarise data?
Measures of central tendency + dispersion
What graph would you make if you had a lot of data?
Frequency distribution plot/graph
Properties that all normally distributed data show
Symmetrical
Equal mean, median + mode
What do Z-scores do?
Describes a values relationship to the mean of a group of values.
How is the z-score measured?
In terms of SD from the mean
Equation to calculate z-score
(X - mean) / SD
Where would z-score of 0 be on a normal distribution curve?
In the middle of the bell curve
What do z-scores + normal distribution curve allow you to identify?
Ind. score rel. to pop
Probability of scoring a given z-score or higher/lower
What score is needed to be in a given % of the pop
What are the important z-scores?
- 96
- 58
- 29
Z-score
1.96
95% of scores fall w/in 1.96 Z scores or SDs above/below mean
Z-score
2.58
99% of scores fall w/in 2.58 Z scores or SDs above/below mean
Z-score
3.29
99.9% of scores fall w/in 3.29 Z scores or SDs above/below mean
Type of deviation from normality
Skewness
A measure of lateral deviation from normality
