Unit 14 Flashcards
Population
set of items that you are interested in
Census
Survey of the whole population
Sample
Smaller number of items from the whole population. A sample of at least 10% is considered to be a good sample
How do you reduce bias
In order to recue bias, the sample must represent the whole population
Random sample
In a random sample each item has the same chance of being chosen
Strata
A population may divide into groups such as age range or gender. These groups are called strata
What is a stratified sample
Number of people taken from each group is proportional to the group size
What does cumulative frequency show
How many data values are less than or equal to the upper class boundary of each data class
What is a cumulative frequency diagram
A cumulative frequency diagram has data values on the x-axis and cumulative frequency on the y axis
How do you find the estimate for the median value
n
– th value
2
How do you find the estimate for the lower quartile
n
- th value
4
How do you find the estimate for the upper quartile
3n
— th value
4
How do you find the interquartile range (IQR)
UQ - LQ
How do you find the lower quartile for a set of n data value
(n + 1)
——– th
4
How do you find the upper quartile for a set of n data values
3 (n+1)
——— th
4
What does a box - plot display
A box plot sometimes known as a cat and whisker diagram displays a data set to show the median and quartiles
What are comparative box plots
Comparative box plots are box plots for two different sets of data drawn on the same scale
What is a histogram
A histogram is similar to a bar chart but is used to represent continuous data
What does the area and height of each bar in a histogram represent
In a histogram the area of the bar represents the frequency
The height of each bar is frequency density
How do u calculate frequency density
class width
What does the interquartile range measure
The interquartile range measures the spread of the middle 50% of the data.
How do you describe a data set
To describe a data set (or population) give a measure of average and a measure of spread.
How do you compare data sets
Compare a measure of average and spread
