Is it possible to find the interquartile range without plotting a cumulative frequency curve?

Answer 1

All you need to do is sort your data numbers in order (or frequencies). Work out what nth value of the numbers is 1/4 of the subtotal of the data (i.e. 1/4 of the number of elements), the number in that position is your lower quartile.
Then do the same to find the 3/4 position and that's the upper quartile number. Take one from the other and you have the range.

Answer 2

In fact, one does not need to calculate or plot cumulative frequency. Quartile is about the number of data points leading up to 25%, 50%, and 75% of the data points in an ordered set of data. The value of the data point at the 50% mark is, by defintion, the median of a data set. This simply means that there half of the data points below that value and half of them above.

Check out:

"Quartile
From Wikipedia, the free encyclopedia
...
In descriptive statistics, a quartile is any of the three values which divide the sorted data set into four equal parts, so that each part represents 1/4th of the sample or population.

Thus:

first quartile (designated Q1) = lower quartile = cuts off lowest 25% of data = 25th percentile
second quartile (designated Q2) = median = cuts data set in half = 50th percentile
third quartile (designated Q3) = upper quartile = cuts off highest 25% of data, or lowest 75% = 75th percentile
The difference between the upper and lower quartiles is called the interquartile range.

Example 1:

Data Set: 6, 47, 49, 15, 42, 41, 7, 39, 43, 40, 36

Ordered Data Set: 6, 7, 15, 36, 39, 40, 41, 42, 43, 47, 49

Q1 = 25.5

Q2 = 40

Q3 = 42.5

Example 2:

Ordered Data Set: 7, 15, 36, 39, 40, 41

Q1 = 15

Q2 = (39+36)/2 = 37.5

Q3 = 40" [See source.]

Answer 3

Yes.

Answer 4

Yes.

Answer 5

No...foolish mortal. Everyone knows THAT! Now, bow before the gods of frequency until they are appeased!

Answer 6

if you have all the data points, then yes