Everything you need to know! Flashcards
What information goes along the horizontal axis of a population pyramid?
Percentage (of the total population)
What are the key features of a stem and leaf diagram?
Key
Numbers in the leaves in order and in line with each other
Stem on the left hand side (or down the middle if it’s a double sided stem and leaf diagram)
How do calculate the mean?
Add up the data items and divide by how many there are
Name three ways in which charts can be misleading.
No scales on their axes
A false origin (the vertical scale doesn’t begin at zero)
Bars not drawn in proportion (i.e. different widths)
Missing axes
What does x with a line over the top (x bar) stand for?
This is the mean of the data set. We use it when finding the standard deviation
How do you find the range of data displayed in a stem and leaf diagram?
Find the smallest number. Find the largest number in the diagram. Work out the difference.
How do you find the mode of data displayed in a stem and leaf diagram?
Find which number occurs most often. Be careful: don’t just look in the leaf. You need to write down the full number i.e. 3 l 7 is 37 not 7
How do you find the median of data displayed in a stem and leaf diagram?
Cross off the smallest and the largest number. Then the next smallest and the next largest number. Keep going until:
a) you have one number left - the median
b) you have two numbers left - the median is the middle of these two numbers
How do you find the mean of data displayed in a stem and leaf diagram?
Just like data in a list, you need to add up the data items and divide by how many there are
When is the mean not a suitable average?
When one number is a long way from the others - because this mean involves adding all numbers up, this situation would make the mean much lower/higher than it should be
Why is this statement misleading?
Sales increased £3 million over the last year
We’re not told what they increased from. £3 million might be a huge increase for a small company or a small increase for a company as big as Tesco
What is primary data?
Data which you collect yourself
What is secondary data?
Data which is collected from published statistics or databases
What are the advantages of primary data?
You know how the data was collected
You know who the data was collected from
What are the disadvantages of primary data?
Time consuming
Expensive