Qualitative Data
Tables, bar chart, pie chart,
Quantitative data
Graph dot plot, stem and leaf plot, histogram, Box and whiskers plot dot plot Read off the actual values from the plot Symmetric: Plot is same as its image under reflection about some vertical line
types of plot
- Right skewed
- Salary, Profit
- left skewed
- marks in exam
- Bimodal distribution
- Mixture of population
Outliers
One or 2 data points are very different from the rest Investigate:
- Mistake in recording (fix it)
- Outlier comes from a different population
- Population is shewed
Stem and Leaf plot
Easy to plot and observe the data can reconstruct the original data
Histogram
Use it when there are too many points to draw a leaf plot then use histogram From histogram we cannot recover the original value Rule of thumbs for number of classes
| observation | classes |
|---|---|
| <25 | 5-6 classes |
| 25-50 | 7-14 classes |
| >50 | 15-20 classes |
| Box and whiskers |
Numerical measure
- Mean
- Median
- Mode
Show that mean minimizes the sum of squared deviations for a set of values