Worksheets › Class 11 › Organisation of Data › Cheat sheet
Class 11 Organisation of Data: cheat sheet
CBSE Social Science. How raw data are classified and grouped into frequency distributions, with class limits, class marks, widths, tally marks and the exclusive and inclusive methods.
Key ideas
- Raw data are data as collected; classification arranges them into groups so that they are easy to compare and analyse.
- Data can be classified chronologically (by time), spatially (by place), qualitatively (by attribute) or quantitatively (by size).
- A continuous variable takes any value in a range (height); a discrete variable takes only certain values (number of children).
- A frequency distribution shows how many observations fall in each class; a frequency array does this for a discrete variable.
- In the exclusive method (10–20, 20–30) a value equal to an upper limit goes in the next class; in the inclusive method (10–19, 20–29) both limits belong to the class.
- Grouping loses detail: each value is treated as if it were the class mark.
Remember
| Class mark | (lower limit + upper limit) ÷ 2 |
| Class width | upper limit − lower limit |
| Number of classes | (largest − smallest) ÷ class width |
| Tally marks | each bundle of five plus the single strokes: 5 × bundles + singles |
| Inclusive to exclusive | lower limit − 0.5 and upper limit + 0.5 (10–19 becomes 9.5–19.5) |
| Cumulative frequency (less than) | add the frequencies of all classes up to that one |
| Percentage frequency | class frequency ÷ total × 100 |
Watch out
- Counting a value equal to the upper limit in the same class under the exclusive method.
- Taking the class width as the class mark.
- Calling the number of rooms continuous (it is discrete).
Worked example
Convert to the exclusive method: (a) 70–79 (b) 90–99. What is the width of each class?
Working: subtract 0.5 from the lower limit and add 0.5 to the upper
Answer: (a) 69.5–79.5, width 10 (b) 89.5–99.5, width 10
Practise Organisation of Data
Revise with this page, then practise: every Organisation of Data sheet in the app is new, with an answer key and working.
Coming soon for Android and iPhone.