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Measures of Variability

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Measures of Variability
Measure of variation is a measure that describes how spread out or scattered a set of data. It is also known as measures of dispersion or measures of spread. There are three measures of variation: the range, the variance, and standard deviation. The range is the true upper limit in a distribution minus the true lower limit. In a visual sense the Range = Highest value – Lowest value. In the sample we were provided, the range for this set of data is 8. This is because the highest value of the sample was 8, and the lowest value of the sample was 0. If I plug the numbers of the data set into the formula, range = 8-0. The answer we receive is 8. The interquartile range is range in a distribution between the end of the first quartile and the beginning of the third quartile. The formula for calculating the IQR is IQR = (QU-QL). Quartiles are the points in a distribution corresponding to the first 25% of the data set, the first 50% of the data set, and the top 25% of the data set. With all this being said, you must first find the quartiles before you find the interquartile range. In the sample that was given our quartiles are as follows: QL (lower quartile) equals 0.75, QM (median) equals 2, and QU (upper quartile) equals 3.5. My next step was to plug these numbers into the IQR formula. IQR = (3.5 –0.75), this makes the interquartile range equal to 2.75.
The variance is a statistic that measures variability of a distribution as the average squared deviation of each data from the mean of all data. The formula for variance isσ2 = Σ (Xi - X) 2 / N (Stat Treck, 2015). In Words, this formula says to take each data and subtract the mean, then square this difference, then sum all these differences, and then divide this sum by N which represents total number of data (Bachman & Schutt, 2014) . For the sample given, the mean is 2.5. Now I am not making a table for the sake of length of time for reading, but the variance came to 5.45.
The standard deviation is the square root of the average squared deviation of each data from the mean. The formula for standard deviation is σ = sqrt [Σ (Xi - X) 2 / N] (Stat Treck, 2015). The standard deviation of the sample that was given is 2.3345.

References
Bachman, R., & Schutt, R. K. (2014). The Practice of Research in Criminology and Criminal Justice. Thousand Oaks, California : SAGE Publication INC.
Stat Treck. (2015). Retrieved from http://stattrek.com/statistics/dictionary.aspx?definition=Variance

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