2 - Meaaures Of Location And Spread Flashcards
(30 cards)
What is a measure of location
A single value that describes a position in a data set
What is a measure of central tendency
A value that describes the centre of the data
What is the mean
The average value of the data
Σx / n
What is the mode
The value that occurs most often
What is the modal class
The class that has the highest frequency
What is the median
The middle value of the data
When is the mode used
In quantitative or quantitative data, where there are only 1 or two modes
When is the median used
Quantitative data, when there are extreme values (extreme values typically dont affect the mode)
When is the mean used
For qualitative data
It uses all the data, so gives the most true measure of data
It is affected by extreme values
How do you calculate the mean in grouped frequency tables
Σfx / Σf
Where x is the midpoint of the class
How do you find the lower quartile of DISCRETE data
n/4.
If this value is a whole number, the LQ is between this data point and the one above
If the value is a decimal, round up and pick this data point
How do you calculate the upper quartile in DISCRETE data
3/4 (n)
If this value is a whole number, the UQ is between this data point and the one above
If the value is a decimal, round uo and pick this data point
What is the lower quartile
The point that is 25% through the data
What is the upper quartiles
A data point that is 75% through the data
How do you calculate the median in discrete data
n+1 /2. = Nth value
If this value is a decimal, find the middle value between this point and the one above it
If the value is a whole number, take that point
How do you estimate median, quartiles and percentiles in grouped frequency tables
Use liner interpolation
What do you have to assume about the data when doing linear interpolation
That the values are evenly distributed in the class
What is the formula for linear interpolation
Lower boundary + (median - cf before/ class frequency ) × class width
If estimating percentiles / quartiles, replace the median value
What are measures of spread ( dispersion / variation)
Measures of how spread out (far apart) that data is
The range and IQR are measures of spread
What is the range
The largest - smallest value
What is the IQR (interquartile tange)
Uper quartile - lower quartile
It tells you the location of 50% of the data
What is the interpercentile range
The difference between values for two give percentiles
What is variance
A measure of spread that shows how far out values are from the mean
(The lower the variance the lower the spread)
What is standard deviation
The root of the variance, it shows how far out values are from the mean
