Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
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: SADC Course in Statistics Module B2 Session 14 – Page 1 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. SADC Course in Statistics Module B2 Session 14 – Page 2 Module B2 Session 14 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. SADC Course in Statistics Module B2 Session 14 – Page 3 Module B2 Session 14 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. SADC Course in Statistics Module B2 Session 14 – Page 4 Module B2 Session 14 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: SADC Course in Statistics Module B2 Session 14 – Page 5 Module B2 Session 14 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. SADC Course in Statistics Module B2 Session 14 – Page 6 Module B2 Session 14 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: SADC Course in Statistics Module B2 Session 14 – Page 7 Module B2 Session 14 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? SADC Course in Statistics Module B2 Session 14 – Page 8 Module B2 Session 14 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. SADC Course in Statistics Module B2 Session 14 – Page 9 Module B2 Session 14 SADC Course in Statistics Module B2 Session 14 – Page 10