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# What is quartile deviation?

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###### 2010-01-23 15:23:27

Quartile Deviation (QD)

The quartile deviation is half the difference between the upper and lower quartiles in a distribution. It is a measure of the spread through the middle half of a distribution. It can be useful because it is not influenced by extremely high or extremely low scores. Quartile Deviation is an ordinal statistic and is most often used in conjunction with the median.

why we calculating quartile deviation?

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## Related Questions

What is mean deviation and why is quartile deviation better than mean deviation?

In a data sample, the purpose of quartile deviation is a way to measure data dispersion instead of using the range. The quartile deviation is found by subtracting the lower quartile from the upper quartile, and dividing this result by two.

The quartile deviation(QD) is half the difference between the highest and lower quartile in a distribution.

Information is not sufficient to find mean deviation and standard deviation.

6,6,9,5,8,9,6,7,8,8,6,5,5,6,8,5,7,7,8,6,5,9,10,14,5,8,5,8,10,10,7,7,7,8,6,6,7,5,7,8,8,5,6,6,7,7,7,6,6,9

we calculate standard deviation to find the avg of the difference of all values from mean.,

Strictly speaking, none. A quartile deviation is a quick and easy method to get a measure of the spread which takes account of only some of the data. The standard deviation is a detailed measure which uses all the data. Also, because the standard deviation uses all the observations it can be unduly influenced by any outliers in the data. On the other hand, because the quartile deviation ignores the smallest 25% and the largest 25% of of the observations, there are no outliers.

There are many:Range,Inter-quartile range,Percentile rangesMean absolute deviation from the mean or medianVarianceStandard deviationStandardised deviation

A quartile deviation from some specified value, is the value or values such that a quarter of the observed values fall between these values and the specified value. Usually, but not always, the specified value is the median - the value such that have the observed values are below (and above) it. In that case, one quartile values will have a quarter of the values below it and the other will have a quarter of the values above it. The quartile deviations will be the differences between median and the two quartiles just calculated.

It is not possible to answer without any information on the spread (range, inter-quartile range, mean absolute deviation, standard deviation or variance).

This helps to show where things may not follow the norm. Quartiles help you to keep data organized and so a deviation would show how it would vary.

Graphing to determine difference between third and first quartile as well as to find the median between the two. Also known as semi-interquartile range.

When you are looking for a simple measure of the spread of the data, but one which is protected from the effects of extreme values (outliers).

If this is the only information you have, the answer would be somewhere around 125. Usually, you would find the third quartile by first finding the median. Then find the median of all of the numbers between the median and the largest number, which is the third quartile.

A simple method is the inter quartile range. A more sophisticated option in the standard deviation.

Standard deviation helps planners and administrators to arrive at a figure that could be used to determine a range that can effectively describe a given set of numerical information/data; and based on which a decision concerning a system of those data can be made.

There are many:Range.Inter [ ] Range : where the middle part may be quartile, quintile, decile or percentile. Other options are possible but less common.Mean absolute deviation.Mean squared deviation (variance).Standard error.Standard deviation.

Standard error, standard deviation, variance, range, inter-quartile range as well as measures based on other percentiles.

the interquartile is just subtracting the high quartile from the low quartile. * * * * * No, it is subtracting the lower quartile from the higher quartile.

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