STATA 11 for Windows SAMPLE SESSION - Food Security Group ...

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Stata 11 Sample Session Section 3 – Tables and other Types of Analysis The output is: Variable| 0 1 2 3 4 5 6 7 8 9 **** . --------+---------------------------------------------------------------------- h35a | 0 86 49 0 0 44 23 1 2 1 1 136 h35b | 0 4 35 1 1 39 8 1 4 1 1 248 h35c | 0 0 1 2 0 2 10 2 1 2 1 322 Other Types of Analyses Weights Using this type of analysis you could state the following: Cotton was the most frequent primary cash crop. 90 households grew this crop, peanuts and rice were the next most often grown for cash. You can also use the tab1 command. tab1 h35* Sub-Command type of weight Definition Stata provides for a method to analyze data using different types of weights. The type of weight that is to be used with a set of data will depend on the type of sampling that has been used. See the table below for an explanation of the available weight types. fweight or frequency frequency weights Number of replicated observations, this value is always an integer. If the fweight associated with an observation is 5, it means the observation represents 5 identical observations. pweight Sampling weights inverse of the probability that this observation is included in the sample due to the sampling design. A pweight of 100 indicates that this observation represents 100 subjects in the population. There are qualifications to this weight when used with survey analysis commands aweight or cellsize analytic weights inversely proportional to the variance of an observation. The observations typically represent averages and the weights are the number of elements that produced the average iweight Importance weights relative “importance” of the observation. This weight is generally used by programmers who want to produce a specific computation. To read more about weights look at the User manual - weights. If you use the generic “weight” sub-command, Stata will tell you which weight it assumes you want to use. Not all commands will allow a weight to be included. The format is 98
Stata 11 Sample Session Section 3 – Tables and other Types of Analysis Indicator variables [type_of_weight=variable_in_file]. Let’s use one of the Stata’s sample data files to explore this subcommand. 1. Click on File then Open A dialog box should open telling you that the data have changed and do you want to continue and lose unsaved data. We don’t want to save any changes to the data file, click on Yes 2. Select census.dta. 3. Click on Ok. - Remember to copy the command and paste it into the do-file editor. Use the Browse button to look at the data. There is one observation for each state. The variable called pop is the total population for the state. The variable called medage is the median age of the population. First let’s get the populationweighted mean. 1. From the Statistics menu select Summaries, tables & tests then Summary and descriptive statistics then Summary statistics The Summarize - Summary Statistics dialog box opens. 2. Select medage in the “variables” box. 3. Click on the “weights” tab. Note that only 3 types of weights are available to choose from. There is also a help button on weights. 4. Select Analytic weights 5. Click on the copy button, switch to the do-file editor, paste the command, switch back to the dialog box and click on Submit. Look at the output. The sum of the weight is 225,907,472. This is the population of the U.S. in the 1980 census. The weighted mean is 30.11. Now, return to the dialog box. 6. Click on None under the Weight tab. 7. Click on the copy button, switch to the do-file editor, paste the command, switch back to the dialog box and click on Ok The unweighted mean is 29.54. The Stata commands are: use "census.dta", clear summarize medage [aweight=pop] summarize medage Survey weights are discussed in the next section. An indicator variable is a special case of a categorical variable. An indicator variable has two groups only, whereas other categorical variables can have more than two groups. Usually 99
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STATA 11 for Windows SAMPLE SESSION - Food Security Group ...

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