1. Tables and graphs for frequencies and summary statistics
Module I3 Sessions 10 to 12

2. Learning objectives Students should be able to:
Produce multi-way tables
of counts and tables with the appropriate percentages
Explain the criteria
that dictate how complex a table needs to be
Produce tables for continuous variables
that include the appropriate summary statistics.
Explain what the margins of a table are
and know when to include the margins in a table.
“Drill-down” to examine the data
that have given rise to the elements of a table.
Produce the charts
that correspond to a given table

3. Contents This presentation initially Review
Uses full demonstration “Describe data well”
Practicals 1, 2 and 3:Counts and percentages
Practical 1 – on demonstration
Practical 2 – uses rice survey
Practical 3 – Survey on Principles of Official Statistics
Presentation continued
Practical 4: Summarising variates in tables
Practical 5: Tables and graphs together
Using the Tanzania case study

4. Objectives from the rice survey
Simple objectives
Not so simple objectives

5. Objectives for different types of variable
Factor, or category, or qualitative variable
Numeric or quantitative variable
Two factors
One numeric and one factor
Two numeric

6. Review and practicals 1 and 2
Look at the demonstration
As a class or in pairs
Do practical 1 at the same time
Then practical 2
Same ideas
Practice using Excel
Introduces a more complicated objectives (next slide)
To understand different percentages
Then review these ideas
Or continue with practical 3 first

7. Review of ideas Practical 1 Practical 2 Practical 3
Reminder of the steps in an analysis
Practical 2
One-way and two-way tables
Which percentage is appropriate?
Practical 3
Frequency tables in general
Tables with and without margins (“totals” in Excel)

8. How to describe data well
Look for oddities in the data
and be prepared to adapt the summaries that you calculate
Study the data as tables and graphs
Use frequencies and percentages
to summarize categorical variables
Use averages and measures of variability
to summarize numeric variables
Identify any structure in the data
and use it in producing your summaries

9. The 2 types of variable are summarized in different ways
Look at the data
The 2 types of variable are summarized in different ways

10. Simple summaries to meet simple objectives

11. Contents of these summaries

12. Does this summary satisfy any of the objectives?
Summary of the yields
Does this summary satisfy any of the objectives?

13. In summary – for the simple objectives

14. What other suggestions were made for coping with outliers?
Checking for oddities
What other suggestions were made for coping with outliers?

15. Answering more complicated objectives
AND explaining some of the variability

16. One-way and two-way tables
One way table – with 2 summary statistics
Two-way table
Margins of the table
The margins of a 2-way table are one-way tables

17. Percentages in tables
Consider carefully which percentage(s) are appropriate
Here “row” percentages compare types of country
Column percentages would compare where implemented

18. Sort of 2-way table? Or one-way table with 9 summary statistics
This margin is meaningless – and should be hidden

19. Tables can be 3-way or higher
Excel gives all the totals
But is more limited in giving percentages

20. Practicals 4 and 5 Practical 4 Practical 5 Rice survey again
Tables for numeric variables
As well as frequencies for factors
Practical 5
Apply the ideas
To the data from Tanzania
Look at power used for lighting (factor)
At size of land holdings (numeric variate)
And at keeping indigenous chickens – both!

21. Tables that summarise variates as well
Objective: How do the yields relate to the variety grown?

22. More one-way tables: summary statistics
Also Lower s.d. for Variety than Village.
Why might that be important?

23. Summary statistics in 2-way tables
How do the yields relate to fertilizer and variety?
i.e. extends to objectives from those stated

24. Tanzania agriculture survey
A huge survey of agriculture in Tanzania
Involving about 1800 enumerators
And a main questionnaire of 22 pages
Given to 3223 households
In the district provided for analysis
A technical report
Describes the process of data entry
And checking
Then there is the analysis
And reporting

25. Data for lighting

26. How large a table do you need?
Are these differences sufficiently large that you need this 2-way table?
If no, then the one-way presentation is simpler
If yes, then perhaps a one-way table/graph hides important information

27. One way table/graph

28. Objectives and many questions
To help the extension service
Improve their service to households keeping chickens
What proportion of households
keeps indigenous chickens?
When they do, how many do they keep?
Are these values roughly the same,
or do they differ by district?
Do they differ by other factors,
in particular the sex of the household head
or the type of agriculture household (Q021).

29. Recap Now have the tools to process
Factors (categorical data)
Using frequencies and percentages
Variates (quantitative data)
Using means and medians
And quartiles, extremes, standard deviations
And proportions (risks), percentiles (return periods)
You also know to use other measurements
to reduce the unexplained variation
And the statistics can be presented
in tables and graphs

30. Good tables for Excel users – a guide
A guide is provided
That summarises how to use tables in Excel
And can be used for reference
It also introduces some additional topics
where we need more than Excel
Other summaries in a table (e.g. medians)
Weights in tables
Multiple responses
That are considered in the next sessions

31. Learning objectives Are you now able to?: Produce multi-way tables
of counts and tables with the appropriate percentages
Explain the criteria
that dictate how complex a table needs to be
Produce tables for continuous variables
that include the appropriate summary statistics.
Explain what the margins of a table are
and know when to include the margins in a table.
“Drill-down” to examine the data
that have given rise to the elements of a table.
Produce the charts
that correspond to a given table

32. In the next sessions we extend these analyses
To handle common problems that occur with many surveys