Variables
Score
- Characteristics
2. The value an individual has on a particular variable
Ratio scale
Quantitative variables for which there is a unit of measurement and absolute zero point
Divided into intervals
Order things being measured
Discrete example
Continuous example
- Number of people in classroom
2. Height
Interval scale
Unit of measurement but no zero
Only Kelvin has zero point
100C not double 50C
Qualitative variables
Discrete
No natural ordering to values of qualitative variables
Ordinal variables
Not on equal interval
Natural ordering
Ordinal scale
Natural ordering
No unit of measurement
Stevens’s hierarchy of scales
- Ratio: natural ordering to values, units of measurement, absolute zero
- Interval: natural ordering, units of measurement
- Ordinal: natural ordering, no units
- Nominal: unordered categories
Psychological construct
An abstract quantity that explains some aspect of behaviour. Intelligence, introversion, sociability
Operational measure of intelligence
Tool to measure psychological construct. Questionnaire.
May derive from speed and accuracy of answering.
Valid
Reliable
- Measures what it’s supposed to measure
2. Similar results many times
Measurement error
Variability in measurements
Inferential statistics
Descriptive statistics
- The act of inferring population parameters from sample statistics
- Do not involve inferences about parameters
Convenience sample
Sampling bias
Sampling error
- Samples conveniently available
- Not all members had an equal chance of being selected in the sample
- Difference between sample statistic and population parameter it estimates
Sampling distribution
A probability distribution of all possible values of a sample statistic based on samples of the same size
