# What is meant by 90 percentile marks

## Percentile

### Percentile definition

The Percentile or the Percentile rank is the percentage of the values ​​of a distribution that is <= a given value.

This can answer the question: What percentage are smaller, lighter, worse ...? - or the opposite question: what percentage is bigger, heavier, better ...?

### example

Of the 25 students in a class, 5 each wrote a grade 1, 5 a grade 2, 5 a grade 3, 5 a grade 4 and 5 a grade 5 in each exam.

For example, if a student has a grade of 2, he or she doesn't necessarily know whether he did really well (maybe everyone else has a grade of 1).

However, if the teacher tells the student with the grade 2 that he is in the 80% percentile, he knows that 80% of the students have a grade 2 or below ("worse") and only 20% above (the 5 students, which have a grade of 1).

The percentile can therefore be used as a benchmark to classify a certain value.

In the example above, the percentile must be determined individually (depends on the distribution of the grades). However, many measured values ​​such as body height are subject to the normal distribution and in this case the percentiles can be read from a table for the standard normal distribution.

Percentiles are often used as a reference to estimate whether values ​​are in the normal / acceptable / uncritical range. For example, the height and weight of children are measured in the regular U-examinations and it is checked whether they are within the so-called percentile curves in the range from the 3rd percentile to the 97th percentile (as the extreme range) at the respective age.

Some percentiles are used by default as statistical measures, e.g. the median as the 50% percentile and the lower or upper quartile as the 25% or the 75% percentile. 