Proc surveymeans t test example

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Proc surveymeans t test example

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Working with Complex Survey Data in SAS

See www. These SAS statistics tutorials briefly explain the use and interpretation of standard statistical analysis techniques for Medical, Pharmaceutical, Clinical Trials, Marketing or Scientific Research.

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The examples include how-to instructions for SAS Software. Statistical options that may be requested are: default statistics are underlined. This example calculates the means of several specified variables, limiting the output to two decimal places. Notice that in this output, PROC means indicates that there is a small value of could be a missing value code and a large value of 78 could be a miscoded number.

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This is a quick way to find outliers in your data set. To compare two paired groups such as in a before-after situation where both observations are taken from the same or matched subjects, you can perform a paired t-test using PROC MEANS.

To do this convert the paired data into a difference variable and perform a single sample t-test. This is essentially a one-sample t-test. The SAS output is as follows:. The t-statistic associated with the null hypothesis is —2. End of this tutorialpart 1, Click to continue. Elliott, email:info texasoft. BoxCedar Hill, TX All Rights Reserved. Other brand and product names are trademarks of their respective companies.

For more information Through its straightforward approach, the text presents SAS with step-by-step examples. It's also a valuable reference tool for any researcher currently using SAS. Designed for those new to SAS and filled with illustrative examples, the book shows how to read, write and import data; prepare data for analysis; use SAS procedures; evaluate quantitative data; analyze counts and crosstabulation tables; and compare means using the t-test.

The book also provides instruction and examples on analysis of variance, correlation and regression, nonparametric analysis, logistic regression, creating graphs, controlling outputs using ODS, as well as advanced topics in SAS programming. ISBN: X. Order From Amazon. Alan Elliott Website.

New to version 8.The purpose of this workshop is to explore some issues in the analysis of survey data using SAS 9.

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This procedure can produce graphs. This procedure does not have a stratacluster or a domain statement, and it does not allow for replicate weights. It requires that a sampling weight be specified at each level of the model. Regular statistical software that is not designed for survey data analyzes data as if the data were collected using simple random sampling.

For experimental and quasi-experimental designs, this is exactly what we want.

proc surveymeans t test example

However, very few surveys use a simple random sample to collect data. Not only is it nearly impossible to do so, but it is not as efficient either financially and statistically as other sampling methods.

When any sampling method other than simple random sampling is used, we usually need to use survey data analysis software to take into account the differences between the design that was used to collect the data and simple random sampling.

This is because the sampling design affects both the calculation of the point estimates and the standard errors of those estimates. If you ignore the sampling design, e. Ignoring the clustering will likely lead to standard errors that are underestimated, possibly leading to results that seem to be statistically significant, when in fact, they are not.

The difference in point estimates and standard errors obtained using non-survey software and survey software with the design properly specified will vary from data set to data set, and even between analyses using the same data set.

While it may be possible to get reasonably accurate results using non-survey software, there is no practical way to know beforehand how far off the results from non-survey software will be. Most people do not conduct their own surveys. Rather, they use survey data that some agency or company collected and made available to the public.

The documentation must be read carefully to find out what kind of sampling design was used to collect the data. This is very important because many of the estimates and standard errors are calculated differently for the different sampling designs. Hence, if you mis-specify the sampling design, the point estimates and standard errors will likely be wrong. Perhaps the most common is the sampling weight. A sampling weight is a probability weight that has had one or more adjustments made to it.

Both a sampling weight and a probability weight are used to weight the sample back to the population from which the sample was drawn.

By definition, a probability weight is the inverse of the probability of being included in the sample due to the sampling design except for a certainty PSU, see below.This example is a continuation of Example Suppose that you are now interested in estimating the gender domain means of weekly ice cream spending that is, the average spending for males and females, respectively. Output Suppose that you want to test whether there is a significant difference for the ice cream spending between male and female students.

You can use the following statements to perform the test:. The variable Gender is used as a model effect. The DIFF option requests that the procedure compute the difference among domain means. These domain means, including their standard errors, are identical to those in Output If you want to investigate whether there is any significant difference in ice cream spending among grades, you can use the following similar statements to compare:.

The CL suboption requests the "MeanPlot" to display confidence. All the differences are significant based on t tests. In Output Comparisons for each pair of domain means are shown by colored bars at intersections of these grids. The length of each bar represents the width of the confidence intervals for the corresponding difference between domain means.

The significance of these pairwise comparisons are indicated in the plot by whether these bars cross the degree background dash-line across the plot. Since none of the three bars cross the dash-line, all pairwise comparisons are significant, as shown in Output Previous Page Next Page. Previous Page.This example uses the momsag data set. This example uses the wloss2 data set.

This example uses the hospsamp data set.

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These totals are used to compute the finite population correction fpc. SAS allows only one number to be supplied on the proc surveymeans statement. Because the totals change from one stratum to the next, we need to supply them to SAS in a data set.

You can include these data in the primary data set or in a secondary data set. In this example, we will use a secondary data set. Also note that the secondary data set can be "collapsed"; in other words, just one line observations for each strata. The variable oblevel is copied from the original data set because SAS requires all of the variables listed on the strata statement to appear in this data set.

In our example, there is only one variable listed on the strata statement, but in other cases, there may be two or more variables listed. This example uses the jacktwn data set and the secondjt data set. Please see the SAS documentation for information on how to create the secondary data sets needed. This example uses the tab7pt1 data set. Note that there may be a typo in the text for the weighted X-sum and the weighted Y-sum.

If you are using SAS version 8, you will need to calculate the ratio by hand by dividing the two sums. However, the standard error cannot be calculated in this way. This example uses the pt data set.

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This example uses the hospslect data set. Page cluster sampling with unequal probabilities: probability proportional to size sampling. To open the file, you need to use SAS 6. Add the name to the first variable and save the file. Note that the data set is printed on pageexcept for the replicate weight variables. This example uses the am amblnce2 data set.Does anyone have a procedure in mind for longitudinal analysis of ordinal data from a complex survey?

I've been searching all over and am having trouble! Suppose I want to see if a teacher used textbook1 in and in I created a difference variable, called t1. How can I test this in surveymeans? I found some documentation saying to use the domain statement, but that doesn't apply here. I don't think I can use surveyreg because I'd need to incorporate fixed and random effects if I ran a model.

Please advise. Assuming that the two variables you are taking the difference of are continuous and you don't also have strata and clusters then that code should give you what you want. But I'm back with a new twist. How about three or more time points? If the data are non-normal then what distribution would you use to describe them?

In this case it is likely that you would need to take a modeling approach if you are going to use SAS. Any suggestions for normally distributed data? I have a time 1 and time 2 continuous measure paired and I am hoping to test if time 2 is different from time 1. I'd do a paired t test if I wasn't using complex survey data. Do you know? Which features do you like?

Sampling of Populations, Third Edition by Levy and Lemeshow | SAS Textbook Examples

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proc surveymeans t test example

Turn on suggestions. Auto-suggest helps you quickly narrow down your search results by suggesting possible matches as you type. Showing results for. Search instead for.In this task, you will use SAS Survey Procedures to calculate a t-statistic and assess whether the mean systolic blood pressures SBP in males and females age 20 years and older are statistically different. In order to subset the data in SAS Survey Procedures, you will need to create a variable for the population of interest.

In this example, the sel variable is set to 1 if the sample person is 20 years or older, and 2 if the sample person is younger than 20 years. Then this variable is used in the domain statement to specify the population of interest those 20 years and older. These programs use variable formats listed in the Tutorial Formats page.

You may need to format the variables in your dataset the same way to reproduce results presented in the tutorial. Use the strata statement to specify the strata sdmvstra and account for design effects of stratification. Use the cluster statement to specify PSU sdmvpsu to account for design effects of clustering. Use the class statement to specify the discrete variables used to select from the subpopulations of interest. In this example, the subpopulation of interest are gender riagendr.

Use the weight statement to account for the unequal probability of sampling and non-response. In this example, the MEC weight for 4 years of data wtmec4yr is used. Use the domain statement to select those 20 years and older sel by gender riagendr. When using proc surveymeans, use a domain statement to select the population of interest. In this example, the systolic blood pressure variable bpxsar is used.

Use the ods statement to output the dataset of estimates from the subdomains listed on the domain statement above. A t-test is used to test whether the mean SBP between males and females obtained in the previous step is statistically significant different.

Request the t-test from the SAS Proc Surveyreg procedure and follow the steps in the summary table below. Use the SAS Survey procedure, proc surveyregto calculate significance. Use the nomcar option to read all observations. Use the class statement to specify the discrete variables used to select the subpopulations of interest i.

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When using proc surveyreg, use a domain statement to select the population of interest. Use a model statement to specify the dependent variable for systolic blood pressure bpxsar as a function of the independent variable gender riagendr.

The vadjust option specifies whether or not to use variance adjustment. Close Window. Use the var statement to indicate variable s for which descriptive measures are requested. Use the data statement to name the temporary SAS dataset all to append the two datasets, created in the previous step, if age is greater than or equal to 20 sel.

proc surveymeans t test example

Use the print statement to print the number of observations, the mean, and standard error of the mean in a printer-friendly format. Use the domain statement to specify the subpopulations of interest. Use the title statement to label the output.In this statement, you identify the data set to be analyzed, specify the variance estimation method, and provide sample design information. If your design is stratified, with different sampling rates or totals for different strata, then you can input these stratum rates or totals in a SAS data set that contains the stratification variables.

Available statistics include the population mean and population total, together with their variance estimates and confidence limits. You can also request data set summary information and sample design information. For more information, see the section Missing Values.

proc surveymeans t test example

See the section Missing Values for more details. See the section Confidence Limits for more details. By default, the procedure displays all continuous variable and all levels of categorical variables. This order is operating environment dependent. By default, the order is ascending. You can separate values with blanks or commas.

Each value must be between 0 and BRR and jackknife variance estimation do not apply to the variance estimation for percentiles.

The SURVEYMEANS Procedure

See the section Quantiles for more details. Each value must be between 0 and 1. BRR and jackknife variance estimation do not apply to the variance estimation for quantiles.

The procedure uses this information to compute a finite population correction for Taylor series variance estimation. If your sample design has multiple stages, you should specify the first-stage sampling ratewhich is the ratio of the number of PSUs selected to the total number of PSUs in the population. If your design is stratified with different sampling rates in the strata, then you should name a SAS data set that contains the stratification variables and the sampling rates.

You can specify value as a number between 0 and 1. The new default is to produce a rectangular table structure in the output data sets. A rectangular structure creates one observation for each analysis variable in the data set. A stacking structure creates only one observation in the output data set for all analysis variables. If your sample design is stratified with different population totals in the strata, then you should name a SAS data set that contains the stratification variables and the population totals.

The statistics produced depend on the type of the analysis variable. If you name a numeric variable in the CLASS statement, then the procedure analyzes that variable as a categorical variable. The procedure always analyzes character variables as categorical. For numeric variables, the keyword MEAN produces the mean, but for categorical variables it produces the proportion in each category or level.

Also, for categorical variables, the keyword NOBS produces the number of observations for each variable level, and the keyword NMISS produces the number of missing observations for each level.

Thus the number of nonmissing and missing observations might not be the same for all analysis variables. See the section Missing Values for more information. If no statistics are requested, the procedure computes the ratio and its standard error by default for a RATIO statement. Table Method-options must be enclosed in parentheses following the method keyword.


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