Presenting descriptive statistics using graphs and tables Flashcards
What is important when trying to work out how to draw graphs?
- What information do you want to present?
- Diagnostic or summary
- What data type?
- Interval or ratio
- Ordinal or nominal
- How many different types of data e.g. no. of variables
What do descriptive statistics do?
- Check for errors
- Describe & summarise
- Spread of the data
- Ensure appropriate analysis
- Check your anticipated result
What are univariate graphs? and give examples
Graphs are only showing one variable e.g. • Pie charts •Histograms • Box plots • Percentiles
When should pie charts be used?
- Ordinal or nominal data types only
- Few categories-no more than 3/4
- Not to be used for interval/ratio data type
When should histograms be used?
- Histograms for ratio/interval variables only
- Too many possible values for each value to get a column of its own
- Collapsed into classes that are of equal width e.g. classes of 5% body fat
- Equal distances
When should bar charts be used?
- Bar charts are for categorical variables
* Have gaps between the columns unlike histograms
When should a box plot be used?
- Ratio/interval variables or for an ordinal level variable with lots of possible categories
- The box plot displays statistics associated with the median
What are the components of a box plot?
- Outlier (possible)
- Largest value that is not an outlier
- Upper quartile
- Median
- Lower Quartile
- Smallest value that is not an outlier
What are other common percentiles?
- Terciles-populaion divided into 3 equal groups
- Quintiles-populaion divided into 5 equal groups
- Decile- populaion divided into 10 equal groups
What can be detected using box plots?
Skewness
Positive- quartiles move to the left as well as median
Negative- quartiles move to the right as well as media
What is bivariate?
Involves two variables
What is bivariate presentation dependent on?
• Dependent on variable type
- Ratio/interval and ratio/interval
- Categorical and categorical (i.e. not ratio/interval)
- Ratio/interval and categorical
How can bivariate relationships be shown?
• A bar chart can display values of one categorical variable broken down by another
- If appropriate, can be stacked
• Box plot
• Scatter graph
• Histograms and pie charts can only display one variable at a time
What can be used to show two categorical (bivariate) data?
Stacked bar charts
What can be used to show ratio/interval and categorical variable (bivariate) data?
Box plots e.g. different box plot for each category to compare on same graph