Measures of location and spread (T2) Flashcards
What is a measure of location?
A single value which describes a position in a data set
What is a measure of central tendency?
The single value describes the centre of the data
How do you calculate the mode?
The most common number
How do you calculate the median?
The middle value
How do you calculate the mean?
Sum of all numbers/ amount of numbers
How do you calculate the mean in a given frequency table?
Sum of the frequencies
When is the mode used?
When data is qualitative or quantitative with either a single mode or two modes
What does bimodal mean?
When something has 2 modes
How useful is the mode?
Not very informative if each value only occurs once
When is the median used?
For quantitative data
How useful is the median?
It is used when there are extreme values - as they do not affect the median
When is the mean used?
Used for quantitative data & uses all the pieces of data
How useful is the mean?
It gives a true measure of the data
However it is affected by extreme values
How does the median split the data?
Into two equal (50%) halves
What else can be calculated with the median?
The location of quartiles and percentiles
Where is the lower quartile?
One-quarter of the way through the data set
Where is the upper quartile?
Three-quarters of the way through the data set
What are percentiles?
They split the data set into 100 parts
The 10th percentile lies one-tenth of the way through the data
How do you find the lower quartile for discrete data?
Divide n by 4 and find the nearest whole number
How do you find the upper quartile for discrete data?
Find 3/4 of n and find the nearest whole number
What is interpolation?
You are assuming that the data values are evenly distributed within each class
When is interpolation used?
When data is presented in a grouped frequency table interpolation is used to estimate the median, quartiles and percentiles
For grouped continuous data, how do you calculate the lower quartile?
Q1 = n/4th data value
For grouped continuous data, how do you calculate the median/Q2?
Q2 = n/2th data value
For grouped continuous data, how do you calculate the upper quartile?
Q3 = 3n/4th data value
What is a measure of spread?
A measure of how spread out the data
What are the two simple measures of spread?
- Range
- IQR
What is the range?
The difference between the largest & smallest values in the data set
What is the IQR?
The Interquartile Range
The difference between the UQ and LQ
How useful is the range?
Takes into account all videos
Can be affected by extreme values
How useful is the IQR?
Not affected by extreme values
Only takes into account middle 50% of the data
What is the interceptile range?
The difference between the values for two given percentiles
What data is usually used in the interceptile range?
the 10th to the 90th interpercentile is often used since it is not affected by extreme values but still considers 80% of the data
