Collecting and Analysing Data Flashcards
For a sample to be reliable, how much of the population must it be of?
At least 10%
What is primary data?
Data I collect myself
What is secondary data?
Data collected by somebody else
What is a frequency diagram?
A bar chart
What is a modal class?
The class with the highest frequency
What is a stem and leaf diagram?
How do you draw a frequency polygon?
Plot the midpoints against the frequency and join the points with straight lines (freqency on the y axis)
How do you find the mean from a class based frequency table?
Add a midpoint of class column
Add a midpoint x frequency column
Estimated mean is midpoint x frequency divided by the sum of the frequencies
How do you estimate the range from a frequency table?
Uppermost value subtract the lowermost value
What is the lower quartile?
Where the bottom 25% of the data is
How do you calculate the lower quartile?
By finding the value 1 quarter of the way up the list
(Sum of items in list + 1) x 0.25
What is the upper quartile?
Shows where the top 75% of the data is
How do you calculate the upper quartile?
By finding the value 3/4 of the way up the list
Median + Lower Quartile = Upper Quartileth item
Number of items in the list x 0.75th item
Label this box plot
What is the cumulative frequency?
The sum of consecutive frequencies
How do you draw a cumulative frequency graph?
Add a cumulative frequency column
In the first row write the frequency of the first group
In the second row, write the frequency of the combined first and second groups
In the third row, write the frequency of the combined first, second and third groups
Plot the upper bound of each class interval on the x axis
Plot the cumulative frequency on the y axis
What is a histogram?
Similar to a bar chart, a histogram is a diagram where the area of the bar gives the frequency, rather than the height. The vertical axis is the frequency density.
How do you calculate frequency density?.
Frequency
Class Width
(Frequency/ Class Width)
How do you draw a histogram?
Add a class width column
Add a frequency density column
Plot the class on the x axis
Plot the frequency density on the y axis
