section 3

Created by

Beth Green

Cards (22)

what are the three columns in a frequency table?
the values and names of the different pieces of data
shows a mark (tally) for each piece of data
frequency - sum of the tally marks
what is a con of grouped frequency tables? 
it's less accurate as the exact values are lost
what type of class intervals are used for discrete and continuous data? 
discrete - gaps between classes (e.g. 1-5, 6-10)
continuous - no gaps (e.g. 1<x<5,5<x<10)
what are two way tables? 
summarises bivariate data (two variables)
what is bivariate data? 
measures two variables - investigates a link between them
how to interpret a table of data  
identify a value or category directly
find a total or calculate a percentage
describe a trend
explaining why part of the table is inconsistent e.g. the value was rounded
what is a composite bar chart? 
it has single bars split into sections which show frequencies for the different categories
what makes up a stem and leaf diagram?  
a stem - e.g. the tens digits
the leaves - e.g. the ones digits
a key - show what the information means
what is a population pyramid? 
made from two bar charts that are back-to-back
used to compare data within two groups
what do the shapes of a population pyramid mean? 
pyramid - higher proportion of younger than older
barrel - younger and older is equal
inverted pyramid - higher proportion of older than younger
what are choropleth maps? 
they split a geographical area into regions and each region is shaded with a colour or pattern
comes with a key
how to draw a pie chart
calculate the angle for each sector: number in category/ total number *360
draw a circle
accurately draw the sectors
Label the sectors
how to compare two pie charts  
make their areas proportional to the populations they represent
use the same area for each unit of data
work out the radius of the second pie chart given the radius of the first pie chart:
work out the area for one unit of data (pieR@2)/number of items
multiply the area for one unit of data by the total number of items for the second pie chart
rearrange area=pieR@2 to find R of the second pie chart
a larger area on a pie chart means... 
more data
what is a vertical line chart? 
like a bar chart with lines
shows frequency distribution for discrete data
what is a frequency polygon? 
drawn from continuous data in a grouped frequency table
plot the midpoint of each class against the corresponding frequency
use straight lines
what is cumulative frequency? 
a running total of the frequencies
what is a cumulative frequency step polygon?
used for discrete data - use horizontal lines between points
what is a cumulative frequency chart?
shows continuous data
plot the cumulative frequency against the highest value in each class
how to estimate a number from a cumulative frequency chart? e.g. estimate the number of plants with a height less than 12.5cm
draw a vertical line from 12.5cm and read of the corresponding cumulative frequency
what are histograms? 
display continuous data from a grouped frequency table '
how to draw a histogram with equal class widths
frequency on the y-axis
suitable scale on the x-axis
draw a bar for each class
no gaps between the bars