Home › Exam notes › SSC CGL › Collection, Classification & Presentation of Data

Collection, Classification & Presentation of Data

Paper-II Statistics (Post-specific) · Statistics Syllabus

Useful for: SSC CGL

Overview

Statistics starts with collecting reliable data, classifying it into groups and presenting it clearly in tables and charts.

Key points

Primary data are collected first-hand; secondary data are taken from existing sources.
Census studies every unit; a sample studies a representative part.
Classification: geographical, chronological, qualitative (attributes) and quantitative (variables).
Class mark = (lower limit + upper limit)/2; class width = upper − lower limit.
Exclusive classes (10–20, 20–30) exclude the upper limit; inclusive classes (10–19, 20–29) include it.

Explanation

Sturges’ rule for the number of classes: k = 1 + 3.322 log₁₀ N.
Cumulative frequency tables give "less than" and "more than" ogives; their intersection gives the median.
Histograms use areas for unequal class widths; frequency polygons join class marks.
Convert inclusive classes to exclusive by adjusting limits by half the gap.

Step by step

Identify the measure or test asked and its formula.
Organise the data (table, totals) before computing.
Interpret the result (sign, size, significance).

Examples

Class mark of 20–30 = 25.
For N = 100 observations, Sturges’ rule gives k = 1 + 3.322 × 2 ≈ 7.6 → about 8 classes.
Frequencies 5, 8, 12 give cumulative frequencies 5, 13, 25.

Traps and advanced points

Trap: Mixing inclusive and exclusive class limits.
Trap: Using bar heights for unequal histogram widths.
Trap: Confusing primary and secondary data.

Quick revision

Class mark = mid-point.
k = 1 + 3.322 log N.
Ogives meet at the median.

Practice MCQs

Choose the odd one out if three numbers follow a common difference of 4: 32, 24, 37, 28.
1. 37
2. 24
3. 32
4. 28
Read chapter notes · Similar questions
Show answer
Answer: (a) 37. The regular terms fit an arithmetic pattern with difference 4; 37 does not.
Choose the odd one out if three numbers follow a common difference of 5: 26, 36, 31, 42.
1. 31
2. 36
3. 26
4. 42
Read chapter notes · Similar questions
Show answer
Answer: (d) 42. The regular terms fit an arithmetic pattern with difference 5; 42 does not.
Choose the odd one out if three numbers follow a common difference of 6: 47, 40, 28, 34.
1. 40
2. 47
3. 34
4. 28
Read chapter notes · Similar questions
Show answer
Answer: (b) 47. The regular terms fit an arithmetic pattern with difference 6; 47 does not.
Choose the odd one out if three numbers follow a common difference of 7: 44, 30, 52, 37.
1. 37
2. 52
3. 30
4. 44
Read chapter notes · Similar questions
Show answer
Answer: (b) 52. The regular terms fit an arithmetic pattern with difference 7; 52 does not.
Choose the odd one out if three numbers follow a common difference of 8: 32, 48, 57, 40.
1. 57
2. 32
3. 48
4. 40
Read chapter notes · Similar questions
Show answer
Answer: (a) 57. The regular terms fit an arithmetic pattern with difference 8; 57 does not.
Choose the odd one out if three numbers follow a common difference of 9: 34, 52, 62, 43.
1. 34
2. 52
3. 43
4. 62
Read chapter notes · Similar questions
Show answer
Answer: (d) 62. The regular terms fit an arithmetic pattern with difference 9; 62 does not.
Choose the odd one out if three numbers follow a common difference of 10: 56, 36, 67, 46.
1. 56
2. 67
3. 36
4. 46
Read chapter notes · Similar questions
Show answer
Answer: (b) 67. The regular terms fit an arithmetic pattern with difference 10; 67 does not.
Choose the odd one out if three numbers follow a common difference of 11: 72, 49, 60, 38.
1. 72
2. 49
3. 60
4. 38
Read chapter notes · Similar questions
Show answer
Answer: (a) 72. The regular terms fit an arithmetic pattern with difference 11; 72 does not.
Choose the odd one out if three numbers follow a common difference of 3: 34, 31, 37, 41.
1. 37
2. 41
3. 31
4. 34
Read chapter notes · Similar questions
Show answer
Answer: (b) 41. The regular terms fit an arithmetic pattern with difference 3; 41 does not.
Choose the odd one out if three numbers follow a common difference of 4: 33, 37, 46, 41.
1. 33
2. 41
3. 37
4. 46
Read chapter notes · Similar questions
Show answer
Answer: (d) 46. The regular terms fit an arithmetic pattern with difference 4; 46 does not.