Objectives and
analysis
Module B2, Session 14
SADC Course in Statistics
Learning Objectives
students should be able to
• Explain some criteria
• for modifying initial objectives, once the data are available
• Explain the importance of specifying
• objectives precisely before starting an analysis
• Be able to outline a simple table or graph
• that corresponds to a stated objective
• Be able to complete a simple table or graph
• given an objective and an outline.
• Review a table or graph to specify
• to what objective(s) this presentation corresponds
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Contents
• Introduction of the ideas
• Sitting in on a review class
• (Flash presentation)
• Practical work
• Using rice survey and the Tanzania survey
• Discussion
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Defining the objectives of the study
• In defining statistics (Session 3)
• Statistics is NOT just collecting numbers
• It is collecting numbers with a purpose
• So, as part of the planning for a study
• You must specify the objectives
• You need this also, before getting a budget!
• Once you have your overall objectives
• You plan the study
• Collect the data
• And get the data ready for analysis
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Analysis objectives
• Before you start the analysis
• You review the overall objectives
• Possibly modify them for the analysis
• Why?
1. Perhaps some objectives are not possible
• Questions may have been misunderstood
• Questions answered in an inappropriate manner
• etc
2. Perhaps new objectives become possible
• A practical complication adds a new objective
• A minor point becomes more crucial
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Overall objectives – small example
• Rice survey
• Two objectives
1. Estimate total rice production
• in the district
2. Investigate the possible relationships
• between production and cultural practices
• and justify the questions in the study
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The district for the rice survey
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The data ready for analysis
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Objectives and measurements
• The objectives led to the questions
• the measurements we took
• 1st objective – total yield in the district
• So we measured the yield on sampled plots
• 2nd objective – relationships with cultural
practice
• so we asked about size of field, fertilizer, variety
• See how the objectives
• lead directly to the questions
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Objectives of the analysis
• Now the data are ready for analysis
• Can we still meet the objectives?
• Possibly – so continue with both parts to the analysis
• But suppose we now realised
• that date of planting was crucial, and not measured
• or there was disease on some fields, not recorded
• Perhaps the 2nd objective is not attainable
• So look carefully at the objectives
• And be prepared to rewrite them
• Or state them more precisely
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Breaking the “curse of variation”!
• Statistics is concerned with studies where
variation is important
• Otherwise you only need a sample of size 1!
• This was discussed in the Concepts Session - Session 3
• Hence also take measurements
• if they may help to explain variation in the data
• even if that measurement is not related to a specific
objective
• Understanding variation in key variables
• like the yield in this rice survey
• Is effectively an objective itself in all statistical studies
• Then the analysis can adjust for these aspects
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Objectives once you see the data
• Sometimes looking at the variables
• permits you to specify objectives
• That’s not as good as starting with them
• But it is still useful
• And the tables and graphs
• Should then follow directly
• From the objectives of the analysis
• This is illustrated in the demonstration
• Look for the following 2 slides in particular
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Tables and graphs to satisfy objectives
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Practical work
• Do practical 1
• It benefits from discussion
• So it is good for students to work in pairs
• First is an demonstration lesson
• This should partly be revision
• Complete the sections in the practical sheet as watch
the lesson
• Then the rice survey data are analysed
• Finally data from the Tanzania agriculture
survey are processed
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The Tanzania agriculture survey
• Here is a second example
• From the Tanzania agriculture survey
• Page 2 of their technical guide
• The details are less important,
• than that the objectives are stated carefully
• and justify the questions in the study
questionnaire
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Overall statement:
Sample census objectives
• The 2003 Agriculture Sample Census was designed
• to meet the data needs of a wide range of users
• down to district level
• including policy makers at local, regional and national levels,
• rural development agencies, funding institutions,
• researchers, NGOs, farmer organisations, etc.
• As a result the dataset is both more numerous
• in its sample and detailed in its scope
• compared to previous censuses and surveys.
• To date this is the most detailed Agricultural Census
carried out in Africa
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The sample census was carried out to:
• Identify structural changes
• if any, in the size of farm household holdings, crop and livestock
production, farm input and implement use.
• Determine if there are any improvements in rural infrastructure
• and the level of agriculture household living conditions;
• Provide benchmark data on production and agricultural practices
• in relation to policies and interventions promoted by the Min. of Agriculture
• and Food Security and others stake holders.
• Establish baseline data for the measurement of the impact
• of high level objectives of the Agriculture Sector Devt Programme (ASDP),
• National Strategy for Growth and Reduction of Poverty (NSGRP)
• and other rural development programs and projects.
• Obtain benchmark data to address specific issues, such as:
• food security, rural poverty, gender,
• agro-processing, marketing, service delivery, etc.
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Analysis to meet objectives
• Overall reports have been produced
• In addition, the data can be used for a
wide range of objectives
• The practical assumes 2 NGOs
• with particular questions
• One is on food security
• The other is on energy for lighting
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Food security
Why is a pie chart a reasonable type of display?
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Food security by district
Why might a stacked bar chart be appropriate?
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Energy use for lighting
Required
1. Decreasing
order
2. With small
categories
combined
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Tables sorted and then grouped
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Horizontal bar chart – for long titles
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Finally:
Are you now able to
• Provide some principles
• that characterise good tables and graphs
• Use these principles
• to recognise examples of good practice
• Suggest reasoned improvements
• for tables and charts
• Provide examples of improved presentations
• Be able to extract points
• from a table or graph for a talk or a report
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In the next session these ideas are
applied to numeric variables
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