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CHAPTER 6: Measures of Dispersion

CHAPTER 6: Measures of Dispersion

- these are statis­tical measures that summarize the amount of spread or variation in the distri­bution of values in a variable.
- the more similar the scores are to each other, the lower the measures of dispersion will be.
- it describes how values are spread within the distri­¬≠bution
- the less similar the scores are to each other, the higher the measures of dispersion will be.
- it also describe how similar a set of scores are to each other.
- in general, the more spread out a distri­bution is, the larger the measure of dispersion will be.

RANGE

- it is the difference between the largest and smallest number in a set of observ­ation.
- the range is rarely used in scientific work as it is fairly insens­itive.
- it is used mostly for quick and easy indication of variab­ility.
- the range can be used when you are presenting your results to people with little or no knowledge of statis­tics.
- it can be used with ordinal or interval- ratio variables.
- two diff sets of data may have same range.
 
1, 1, 1, 1, 9 vs 1, 3, 5, 7, 9

Range Formula:

Ungroup data
Group Data
Range= Highest Score - Lowest Score
Range= Highest Class Mark - Lowest Class Mark

INTER- QUARTILE RANGE (IQR)

- it is defined as the difference of the first and third quartile of a data set.
- it is a measure where the "­middle fifty" lies in the data set.
- therefore, because it uses the middle 50%, it is not affected by outliers or extreme values.

INTER- QUARTILE RANGE (IQR)

INTER- QUARTILE RANGE (IQR)

INTER- QUARTILE RANGE (IQR)

Q3 = also known as UPPER QUARTILE
Q1= also known as LOWER QUARTILE

INTER- QUARTILE RANGE (IQR)

 

CHAPTER 6: Measures of Dispersion

2 IMPORTANT MEASURES OF DISPERSION
- variance
- standard deviation

VARIANCE

VARIANCE

VARIANCE

VARIANCE

VARIANCE

STANDARD DEVIATION

STANDARD DEVIATION

STANDARD DEVIATION

 

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