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Tables and graphs for frequencies and summary

statistics

Module 1 Sessions 5/6

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Learning objectives

Participants 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

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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

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Objectives from the rice survey

Simple objectives

Not so simple

objectives

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Objectives for different types of variable

Factor, or category, or qualitative

variable

Two factors

Numeric or quantitative

variable

One numeric and one factor

Two numeric

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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

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Review of ideas

Practical 1 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)

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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

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Look at the data

The 2 types of variable are summarized in different ways

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Simple summaries to meet simple objectives

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Summary of the yields

Does this summary

satisfy any of the

objectives?

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In summary – for the simple objectives

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Checking for oddities

What other suggestions

were made for coping with

outliers?

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Answering more complicated objectives

AND explaining some of the variability

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One-way and two-way tablesOne way table – with 2 summary statistics

Two-way table

Margins of the table

The margins of a 2-way table are one-way tables

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Percentages in tablesConsider carefully which percentage(s) are appropriate

Here “row” percentages compare types of country

Column percentages would compare where implemented

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Sort of 2-way table?

Or one-way table with 9 summary statistics

This margin is meaningless – and should be hidden

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Tables can be 3-way or higher

Excel gives all the totals

But is more limited in giving percentages

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Practicals 4 and 5

Practical 4 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!

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Tables that summarise variates as well

Objective: How do the yields relate to the variety grown?

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More one-way tables: summary statistics

Also Lower s.d. for Variety than Village.

Why might that be important?

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Summary statistics in 2-way tables

i.e. extends to objectives from those stated

How do the yields relate to fertilizer and variety?

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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

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Data for lighting

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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

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One way table/graph

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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).

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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

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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

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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