Tables and Graphs Flashcards
What are the guidelines for producing good tables?
- Clear title
- Well labelled columns/rows
- Include units of measurements
- Include notes of explanation where necessary
- Include a source of data
- Be well laid out and presented
- Have consistent use of decimal places within a variable
- Include relevant totals/ subtotals that add up
- Should stand alone
What are percentage tables?
Convert counts into percentages
Useful when categories have different sample sizes
Calculate percentage by dividing number in group by total
What are the rules for percentage tables?
Always think about whether you need row or column percentages to answer the question
Make it clear which way the totals add up including 100% totals
Allow somebody to work back to the original sample size either including cell or total n (number)
Why do we use graphs?
Easier to visualise patterns and trends than numbers in a table
Particularly effective in presentations because only limited time for an audience to digest info
An effective way of highlighting a particular aspect of your findings
What are the guidelines for categorical data?
Bars rectangular, of the same width with height proportional to frequency/ percentage
Bars should not touch but can touch in multiple bar charts if the have the same X axis category
Ordering of bars by logical order by the height of the bar
Try not to include more than 3 bars on a multi bar chart
What are stacked bar charts?
Categories within categories
Can display counts or percentages
For percentages the categories must add up to 100
Not the most useful when there is lots of categories
What are pie charts?
100% = A whole circle
Need to convert percentages to proportions divide by 100
Multiple by 360
What are the limitations of pie charts?
- They are effective for displaying the relative frequencies of a small number of categories- not good when you have multiple categories
- Pie charts can be confusing when they are used to compare the outcomes of 2 different experiments
- If based on small number observations can be misleading to label with percentages
- Avoid 3D pie charts as they distort proportions of each category
What is an array?
Ordering the data in ascending or descending order
What are stem and leaf plots?
Makes frequency distribution more visual and gives an idea of the shape of a distribution
Numbers must be evenly placed to get a sense of distribution
Column to the left is the stem (tens) and those to the right are the leaves (digits)
Stems can have multiple digits but leaves only have one
Can draw back to back stem and leaf plots sharing a a stem to compare distributions
Can identify whether data are concentrated around the middle or skewed
Displays all data but time consuming with large samples
What are histograms?
Only shows counts or percent falling within a category, not all data
As categories are continuous, bars should be joined
Bar height represents frequency or %
Bar width represents width of a category, so equal categories have equal widths
How do we represent continuous data with multiple categories?
Categories usually on the x axis
Make sure scales are not misleading
Start Y axis at zero or make it clear that it doesn’t
Distinguish different categories with colours
Statistics used should be in the figure legend
Can use column chart or boxplot
Can add error bars or individual values
How do we represent continuous data with time series?
Best to use a line graph for data on a variable over time
Time should be measured on the horizontal axis
No misleading scales - Y axis at 0 or clear it isn’t
Scales should be the same when comparing to other graphs
Use colours to distinguish
Include SD or SE
What is standard error?
Shows how confident you are in your estimate of the mean
SE = SD/ square root of n
SE will get smaller with a greater sample size, SD won’t
What are scatterplots?
Two continuous variables
Show the relationship between 2 variables
Scales should be clear and appropriate
Distinguish between groups with different colours
How are graphs misused?
Doesn’t reveal what the data conveys.
Improper use of the vertical and horizontal axes leads to distortions
3D charts are bad
Use of infographics - not good for stats
What are the basic guidelines for graphs?
The graph should not distort the data
The graph should not contain unnecessary adornments
Any 2D graph should contain a scale
The scale on the vertical axis should be at 0 unless justified
Label axis
Title
Simplest possible graph used for a given data set
