Biostat Mod 6: Measures of Location: Percentiles, Deciles, Quartiles

Measures of location (or fractiles/quantiles)

Values below which a specified fraction or percentage of the observations in a given set must fall

Percentiles

area under curve divided into 100 equal parts

Deciles

area under curve divided into ten equal parts

Quartiles

area under curve divided into four equal parts

P1

The first percentile, value below which 1% of the values fall

P2

The second percentile, value below which 2% of the values fall

P99

The ninety-ninth percentile, value below which 99% of the values fall

Q1

The first quartile, value below which 25% of the values fall

Q2

The second quartile, value below which 50% of the values fall

Q3

The third quartile, value below which 75% of the values fall

D1

The first decile, value below which 10% of the values fall

D2

The second decile, value below which 20% of the values fall

D3

The third decile, value below which 30% of the values fall

D5

The fifth decile, value below which 50% of the values fall

D6

The sixth decile, value below which 60% of the values fall

D8

The eighth decile, value below which 80% of the values fall

P3

The third percentile, value below which 3% of the values fall

P5

The fifth percentile, value below which 5% of the values fall

P50

The fiftieth percentile, value below which 50% of the values fall

P55

The fifty-fifth percentile, value below which 55% of the values fall

P60

The sixtieth percentile, value below which 60% of the values fall

P80

The eightieth percentile, value below which 80% of the values fall

P87

The eighty-seventh percentile, value below which 87% of the values fall

P93

The ninety-third percentile, value below which 93% of the values fall