Measures Of Dispersion Flashcards
What is the range of a set of data
Range = Highest value - Lowest value
How do you calculate Q1 (the lower quartile)
Q1 = n/4th term
How do you calculate Q3 (the upper quartile)?
Q3 = 3n/4th term
For a continuous grouped data, what must you do to find Q1, Q2 or Q3?
Interpolate.
For interpolation what is on the top and bottom of the line?
Top = class boundaries (which must be extended if there is a gap)
Bottom = cumulative frequency
How can the interquartile range be calculated?
IQR = Q3 - Q1
How can the xth percentile, Px be calculated?
Px = xn/100th term where n is the number of terms
State the equation for the inter-percentile range for n% to m%?
IPR = Pm - Pn
What is variance? (Way to remember the equation)
“Mean of the squares minus the square of the mean”
What is standard deviation? (Equation)
Standard deviation = (Variance)^1/2
For a frequency table or grouped frequency distribution, how do the values for n and x change in the variance equation?
n = sum of the frequencies
x = sum of (fx)
How does coding affect the standard deviation?
Adding or subtracting = no affect
Multiplying or diving = does affect
How can the mean of a combined set of A and B be calculated?
Mean = (n1x1 + n2x2) / (n1+n2)
Where x is the mean and n is the number of values
Under what circumstance would it not matter what measure of location is used to describe data?
If data is symmetrically distributed, or has zero skew, it doesn’t matter whether the mean or median is quoted.
What condition would the median be best to represent distributed data?
If the data is skewed.
