Ogive
Also called: Cumulative frequency curve · Topic: Economic Data: Census, NSS, Surveys and Statistical Tools · NCERT: Class 11, Ch 4 "Presentation of Data"
Meaning
An ogive, or cumulative frequency curve, plots cumulative frequency. Cumulative frequency is a running total of frequencies up to or beyond a point. There are two types:
- The "less than" ogive plots cumulative totals against the upper class limits. It rises from left to right and never falls.
- The "more than" ogive plots them against the lower class limits. It never rises. The two ogives cross at the median, so the median can be read from a graph. An ogive can also give quartiles and percentiles.
Example
For NCERT's marks of 100 students, the "less than" totals are 1 (below 10), 9 (below 20), 15, 22, 43 (below 50) and 66 (below 60). The 50th student therefore falls in the 50-60 class. The ogives cross at about 53 marks, which matches Median = 50 + [(50 − 43)/23] × 10 ≈ 53.
Don't confuse with
- Histogram: this plots plain class frequencies and gives the mode, not the median.
Related concepts
- Raw data
- Classification
- Chronological classification
- Spatial classification
- Qualitative classification
- Quantitative classification
- Attribute
- Continuous variable
- Discrete variable
- Frequency