Describing Data: Graphical Presentation - Explained Notes
1. Types of Data
- Categorical: labels/groups (eye color, marital status).
- Numerical: numbers. Discrete=countable, Continuous=measurable.
2. Graphs for Categorical Data
- Frequency Table: summarizes counts by category.
- Bar Chart: separated bars compare categories.
- Pie Chart: shows percentage of whole.
- Line Chart: used only when data changes over time.
3. Frequency Distribution (Numerical Data)
A table grouping numerical values into intervals (classes).
Steps: sort data, find range=max-min, choose 5-15 classes, class width=range/classes (round up),
count observations.
Example: Range=58-12=46, 5 classes => width≈10.
4. Histogram
Graph of a frequency distribution. Bars touch because numerical intervals are continuous.
5. Cumulative Frequency & Ogive
Cumulative frequency is running total. Ogive is the graph of cumulative frequency/percentage and
is useful for medians and percentiles.
Key exam tips:
- Bar chart: categorical, gaps between bars.
- Histogram: numerical, no gaps.
- Pie chart: parts of a whole.
- Line chart: trends over time.
- Frequency distribution organizes raw numerical data.