- interval/ratio data = normally distributed
- there are three methods to describe data
- three levels of measurement match the three methods of describing data to form a matrix
Statistics method/levels matrix:
| Central tendency | Variability | Graphics | |
|---|---|---|---|
| Nominal (categories: male/female) | mode; "the most frequently occurring value was..." | what are the groups? what is the frequency of each category? | bar chart |
| Ordinal (rank) | median; could also use mode, but not mean | range; "the rankings range from one to 200" | histogram for range of big value pool; bar chart for frequency of small number values |
| Interval/ratio | mean; could also use mode and median but are not very likely to do so | standard deviation (measure of distance from the mean); variance (standard deviation squared) | histogram (is usually based as core/background of normal distribution curve) |
What is correlation?
How one changes with the other. ex: Pearson's correlation coefficient
Descriptive practice using NELS-88 data
standardize the following:
- In SPSS, click Analyze -> descriptive statistics -> frequencies -> move mother education to the right & move move comprehensive race to the right
- For mother ed and race, keep "Display frequency tables" checked. Select median and mode in the statistics button, and bar chart with frequencies in the charts button.
- For reading score, uncheck the "Display frequency tables" checkbox; in statistics button select mean, standard deviation, skewness, and kurtosis; and in charts button select histogram
* with continuous data like test scores, generating a frequency table or bar chart is a waste of time
** with continuous data like test scores, always generate skewness and kurtosis