Decile
Topic: Economic Data: Census, NSS, Surveys and Statistical Tools · NCERT: Class 11, Ch 8 "Use of Statistical Tools"
Meaning
Deciles are the nine values that split ordered data into ten equal parts. Each part holds 10% of the observations.
- D1 marks off the lowest 10%.
- D9 marks off the lowest 90%.
- The fifth decile equals the median: D5 = Q2 = P50.
For ungrouped data, the k-th decile is the size of the k(N+1)/10-th item. Deciles are partition values, like quartiles (four parts) and percentiles (100 parts). They help show how income or spending is spread from bottom to top.
Example
Rank the incomes of households from lowest to highest. The first decile is the income below which the poorest 10% of households fall. MoSPI's HCES reports monthly per capita consumption expenditure (MPCE) by such fractile classes, from the bottom 5% to the top 5%.
Don't confuse with
- Percentile: this divides data into 100 parts, not 10. Scoring at the 82nd percentile means 18% scored higher. The 10th percentile equals the first decile.
Related concepts
- Measures of central tendency
- Arithmetic mean
- Weighted arithmetic mean
- Median
- Quartiles
- Percentiles
- Mode
- Bimodal and multimodal distribution
- Modal class
- Relative position of mean, median and mode