If you have the x-th percentile, the index from a sample of size n that corresponds to it is k := max { i - natural | i <= x*n/100 }. Algorithmically, this is to sort the array and take the element k := floor(x*n/100).
A single number cannot have a percentile.A single number cannot have a percentile.A single number cannot have a percentile.A single number cannot have a percentile.
A percentile depends on the distribution of the observations, not the total number of observations.
Let x be a real number, such that 0 < x < 100. x-th percentile from a sample of n is number k such that k max(i - natural number | i < x.n/100).
You cannot. The 75th percentile is the value of a variable such that 75% of the observations are below that value and 25% are higher. The 75th percentile in the heights of adult women will be a measure of height whereas the 75th percentile in the income distribution in a country will be the level of income [in some currency unit] such that 75% of incomes in the country are lower. These examples illustrate that the 75th percentile can be a measurement in any unit and converting to a percentage makes no sense.
A standard deviation in statistics is the amount at which a large number of given values in a set might deviate from the average. A percentile deviation represents this deviation as a percentage of the range.
A single number cannot have a percentile.A single number cannot have a percentile.A single number cannot have a percentile.A single number cannot have a percentile.
A percentile depends on the distribution of the observations, not the total number of observations.
Let x be a real number, such that 0 < x < 100. x-th percentile from a sample of n is number k such that k max(i - natural number | i < x.n/100).
Oh honey, bless your heart. The 75th percentile means that 75% of the data falls below that number. So, if you have 100 data points, the 75th percentile would actually be the 75th number in order. In this case, 61-70 would be the 70th percentile, not the 75th.
You cannot. The 75th percentile is the value of a variable such that 75% of the observations are below that value and 25% are higher. The 75th percentile in the heights of adult women will be a measure of height whereas the 75th percentile in the income distribution in a country will be the level of income [in some currency unit] such that 75% of incomes in the country are lower. These examples illustrate that the 75th percentile can be a measurement in any unit and converting to a percentage makes no sense.
You would need to know how many questions were on the original test and what number of questions correct would be in the 8.6 percentile. Most tests do not give this data. If you can find it out, then number right / total number on test x 100 gives the percentage. 50 percentile might mean a 70% if it was an average test, or for a hard test 10 percentile might mean a 30%. Without the above information you cannot directly convert one to the other.
You would need to know how many questions were on the original test and what number of questions correct would be in the 8.6 percentile. Most tests do not give this data. If you can find it out, then number right / total number on test x 100 gives the percentage. 50 percentile might mean a 70% if it was an average test, or for a hard test 10 percentile might mean a 30%. Without the above information you cannot directly convert one to the other.
A standard deviation in statistics is the amount at which a large number of given values in a set might deviate from the average. A percentile deviation represents this deviation as a percentage of the range.
percentile
The 20th percentile is an estimate of the value in which 20% of the observations should fall below this value and 80% should be above it. Methods vary on the calculations, but all methods will give similar results if there are a large number of values. See: http://en.wikipedia.org/wiki/Percentile
You can't convert that directly. To convert percentages - or any kind of numbers, for that matter - to percentile, you need to use the definition of percentile. For example, if you have a grade of 90%, you check how many other grades have less than 90%, and divide that by the total number of grades. Note that for example with a grade of 90%, your percentile can be anywhere between 0 and 100 - depending what grades OTHERS had.
75th percentile