Classification, Tabulation and Presentation of Data
What the domain covers
This domain tests classification of raw data, construction and interpretation of frequency distributions, parts of a statistical table, and choice of diagram. Classification may be qualitative, quantitative, temporal or spatial. A frequency distribution shows values or class intervals with corresponding frequencies.
Core rules
- Inclusive classes (10–19, 20–29) have a gap; exclusive classes (10–20, 20–30) do not. Convert inclusive to exclusive with lower boundary = lower limit − 0.5 and upper boundary = upper limit + 0.5 when the gap is 1.
- Class mark = (lower limit + upper limit)/2 for exclusive classes; for inclusive classes use limits or boundaries consistently.
- Class width for exclusive classes = upper limit − lower limit; for inclusive classes = upper limit − lower limit + 1.
- A table needs a number, title, stub, caption, body, source note and footnote where relevant.
- Histogram requires continuous classes; unequal widths require frequency density. Pie-chart angle = (component/total) × 360°.
Worked example
Classes 10–19 and 20–29 are inclusive. Boundaries become 9.5–19.5 and 19.5–29.5. For 10–19, class mark = (10 + 19)/2 = 14.5 and width = 19 − 10 + 1 = 10; using boundaries gives width 10 as well. The distribution is now exclusive and can be graphed as a histogram.
Traps
Writing boundaries as 9–19 or 10.5–19.5 is a common error. Do not plot a histogram for qualitative data. Open-end classes distort means and graphical work; state the assumption used. In pie charts, angles must total 360°, not 100°.