Download Setting and using the objectives

Module B2 Session 14
Practical: Setting and using the objectives
Overall
This is a useful practical to do in pairs, so you discuss the materials at the same time.
It first uses the demonstration in Flash, and then examines tow datasets, the rice
survey, and the Tanzania Agriculture survey.
1. The review lesson
As you watch the review lesson (it is an interactive Flash demonstration) complete the
items listed below:
Screen 1 gives 5 points concerned with “Describing data well”.

Complete the points started below:
How to describe data well
1.
Look for any oddities in the data and …
2.
Look at the data using …
3.
Summarise categorical variables using …
4.
Summarise numerical variables using …
5
Identify any structure in the data, and …
Screen 2 is where the students look at the data.

Which are the factor (categorical) and numeric variables? Give the number of
levels for each of the factor columns.
Factors:
Numeric:
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Module B2 Session 14
Screen 3 presents a 5-number summary of the yield column. You already met this
summary for these data in the SSC-Stat tutorial (Session 11).

Complete the table below:
Summary
statistics
Percentage
point
Number of observations
(out of 36) less than this
value:
Minimum
0
Lower quartile
25%
Median
Upper quartile
Maximum
You are given the 5 numbers: 12, 15, 8, 11, 17 and told that the mean = 12.6.

Explain how this was calculated (remember, if ever a term is unfamiliar, you
can always refer to the statistical glossary introduced in session 3)
Screen 4 gives some objectives, chosen by the students. They are shown in the table
below:

Explain why the first 5 objectives were said to be simpler than the last 3.
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The first 5 objectives are simpler
because …
Screen 5 gives the summary tables and graphs shown below:


Which objectives do they satisfy?
The words “How many” could be interpreted as asking for a frequency, or a
fraction or a proportion (or percentage). Complete the text below with
possible words.
The first table satisfies ____________
The smallest 2 villages in the sample are
from Kesen and Niko. Between them they
have ___ third of the 36 observations.
The other 3 figures satisfy _________
__________________
The third objective in screen 4 (see the figure above), asks “How many farmers use
fertilizer?

Give the answer as a fraction, that could be reported in the text. Do this by
counting the number of zeros in the data (in screen 1) or from the Rice
Survey’s excel file.
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
Outline the table to give the number (and the proportions of farmers applying
fertiliser in 3 categories, 0, (between 0.5 and 1.5) and (2 or more).
Category
Number
Proportion or percentage
0
0.5-1.5
2 or more
Overall

Then (again by just counting), complete the table
Screen 6 finally reviews the main steps in a good description of data.

What is the message when you click on “And remember…”
2. A further objective
In this module we have considered mainly simple (one-way) tables and the associated
graphs. But the ideas of specifying an objective and then getting the resulting table and/or
graph is general.
The first of the more complicated objectives was to find “How many farmers in each
village grow each variety.

Outline this table below, without putting any numbers in.
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
How many rows does your table have? ______



And how many columns? ____________
How do your answers correspond to the number of levels of each factor?
And what numbers will you display in the table (e.g. frequencies or
percentages)?
If you used Excel with its Wizard then one screen is as follows:

From your answers above, complete this screen below by hand?
Complete the screen by:
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3. Constructing the tables and graphs
Once you can outline a table (or a graph) the construction is simpler.


Open the dataset Rice Survey.
Construct the table for the first objective (number of farmers in each village.
Give both the frequencies (counts) as in the previous exercise, and the
percentages. Display the two statistics side-by-side, as in the second table
above.

Make notes on any points that were difficult. Or comment “straightforward for
those that were.
Use Excel to answer the objective relating to fertilizer. First, as asked above “How many
farmers use fertilizer?”
One way is to treat the fertiliser column as a factor and get a pivot table.

Give the counts of the fertilizer column and give it twice, to provide the
counts and the percentages. It should be as follows at least after tidying:
What is your answer, both as a count and a
percentage?
Note any difficult steps
Next, add to the objective, by giving the results for the 3 categories of fertilizer, namely
zero, 0.5 to 1.5, 2 or more.
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You can do this by right clicking in the table and choosing:


Group and Show detail> Group
Enter Start 0.5, End 3, By 1.5.
Look at the full set of data to check whether 0.5 – 2 includes the values of 2, or just values
less than 2?:
How did you check what 0.5-2 means. For
example is it values less than 2 (<2) or ≤2?
Then tidy the table so the results are clear.
4 A larger survey
Open the dataset Tanzania Agriculture Survey and use the sheet called R00.
An NGO has questions on 2 themes. They would like to know what proportion of
households in this region had problems in satisfying food need last year. This is the
variable Q3463 and corresponds to the question:
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

Outline a table to provide this information. Would you give the counts and
the percentages in the table, or just one of them?
You are also asked for a chart to use in a presentation. Explain why you think
a pie chart, such as is shown above, might be appropriate.
Produce the table and chart in Excel. Make sure the order of the results is the same as in
the question.
They return to say that their objectives included knowing in which districts there were the
greatest problems of satisfying food needs.
Outline the table you would suggest. What sort of chart would you now recommend is
now appropriate and why?
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5. Energy for lighting
A second NGO is interested in the energy use, particularly for lighting. They have seen the
question below:
They require a simple table, in decreasing order of the frequency of energy used for
lighting. They would also like to have the table as simple as possible, so categories with a
small percentage of users are grouped together.
They also suggest a pie chart. Explain to them why a horizontal bar chart might be a better
option and produce the table and chart for them.
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