Representing data Flashcards
What makes up data?
Observations/measurements, each recording a value of a particular variable.
What is a qualitative variable?
A variable that takes non-numerical values (e.g. names, colours).
What is a quantitative variable?
A variable that takes numerical values (e.g. height, age).
What is a discrete quantitative variable?
A variable that can only take certain values - there are ‘gaps’ between possible values (e.g. you can’t take a shoe size of 9.664)
What is a continuous quantitative variable?
A variable that can take any value within a particular range (e.g. height or mass)
What is an upper class boundary?
The largest data value that would be included in that class. (If the data is continuous the upper class boundary of a class will be the same as the lower class boundary of the next class.)
What is a lower class boundary?
The lowest value that would be included in that class.
How do you find the class width of a class?
upper class boundary - lower class boundary
How do you find the midpoint of a class?
(lower class boundary + upper class boundary)/2
How do you plot a frequency polygon?
Take the midpoint of each class. Plot the midpoints on the x-axis and the corresponding frequency on the y-axis
How do you find the frequency density?
frequency/class width
How do you plot a histogram?
Plot the values of the variable on the x-axis and the frequency density on the y-axis. Plot boxes the width of the class width and height of the frequency density.
How do you find frequency on a histogram?
The area of a box shows the frequency for that class width.
How do you find the proportion of data values in a class from a histogram?
area of class/total area of all bars
How do you draw a stem and leaf diagram?
Find the lowest common digit and use this and the digits above as the stem. Use the leftover digits for the leaves. Always write a key.
