Aug 9, 2010

Is the longitudinal panel data available for Monitoring the Future?

The information below comes directly from Monitoring the Future. Please refer to their Web site for more information.

  1. A subset of high school seniors are selected each year for follow-up, which is conducted in an alternating biennial fashion, with the first half of the subset receiving their first follow-up questionnaire one year after high school, and the second half receiving their follow-up two years after high school. They receive a series of six questionnaires within this arrangement, so the second half of the subset is 12 years past high school when they receive their last young adult "FU-12" questionnaire. Then, the follow-up procedure changes to 5-year intervals to cover middle adulthood.
  2. The questionnaires in the young adult follow-ups are directly comparable to the base year questionnaires, both in content and in numbers of questionnaire forms. The core drug use questions are included along with the same types of related attitude and behavioral items, many of which are unique to each form, so respondents receive the same questionnaire form throughout the base year and young adult follow-up series.
  3. All data for a particular individual are linked (or, in the case of form-specific items, capable of being linked) in the panel dataset. The sheer amount of information greatly increases the risk of breaching confidentiality. Thus, based on policies approved by our funding source and IRB, the panel data set cannot be made available to the public in totality and without modification.
  4. Special data requests can be made through the Web site email address. Once we get a request, information about policies and procedures is sent out. Requests are considered on a case-by-case basis, and may be fulfilled - at requestor's cost - typically by providing data analytic access.

Additional information about the design of the panel component of the design and procedures used in the study are included in our annual NIDA report, Volume II, and in more detail in the MTF "Occasional Papers." See, for example, "The Aims and Objectives of the Monitoring the Future Study and Progress Toward Fulfilling Them as of 2006" (pdf).

To make a request for this data and for further information, please contact MTF staff at: MTFinfo@isr.umich.edu

What are Quick Tables?

Quick Tables are streamlined data analysis tools that allow you to produce analytic tables by choosing from among pre-selected high-interest variables in drop-down menus. Currently, Quick Tables are available for the following series: HBSC, NSDUH, TEDS-A, and TEDS-D.

Aug 5, 2010

What enhancements are available when using SDA?

SAMHDA recently upgraded the Survey Documentation and Analysis (SDA) system to version 3.4. All of the previous statistical procedures are still available. Users who prefer to use the original interface may still use it by selecting the link entitled Use Classic Interface in the upper-left corner of the screen. SDA 3.4 improves the calculation of statistics for complex samples in the TABLES and MEANS programs.

For the TABLES program, enhancements include:

  1. Corrections to the calculation of standard errors and confidence intervals.
  2. Addition of Rao-Scott F-tests.
  3. Ability to display weighted or unweighted N of cases.
  4. Option to set the number of decimals for all statistics.

For the MEANS program, enhancements include:

  1. Corrections to the calculation of the standard errors and confidence intervals.
  2. Option to display the p-value of each difference from the cells in a base row or column.
  3. Default reporting of the weighted N of cases in each cell for weighted analyses.
  4. Option to include charts in output.
  5. Optional diagnostic table for design variables.

Further information is provided in the SDA Manual (SDA 3.4).

SDA 3.3, released in June 2009, contained the following changes to the analysis programs and features:

  1. Disclosure Protection: SAMHDA now has the ability to suppress output that may compromise the confidentiality of survey respondents by applying disclosure protection rules to a data file. Analysis programs, including RECODE and COMPUTE, now check for the presence of disclosure rules and enforce them. Disclosure rules may be specified to: a) prevent an analysis from being run; b) suppress the output after running an analysis; and c) suppress the unweighted number of cases from being reported in the output. The SDA 3.3 Documentation for Disclosure provides greater detail on the disclosure rules that may be specified.

  2. List Created Variables - View Button: The output from the listing of recoded and computed variables now includes a "View" button that provides access to descriptions of the variables. This feature can be accessed under the SDA Create Variables menu.

  3. Title: A title or label can be entered for each analysis request and will appear at the top of the HTML output produced by SDA analysis programs.

  4. Customized Subset: This procedure has also been revised in that recoded and computed variables may now be included in a subset. If pre-set selection filters have been defined by SAMHDA, these filters now apply to the interactive version of the subset procedure as well as to the analysis programs. A Comma Separated Values (CSV) file is available for output.

Content adapted from the SDA Manual (version 3.3).

For further information on SDA, please select the Getting Started button located in the upper-right portion of the screen or visit the SDA Tutorial.

What are the main components of the SDA interface?

In 2008 SAMHDA upgraded the appearance of the Survey Documentation and Analysis (SDA) system. The new interface allows users greater navigational ability within SDA. All of the statistical procedures are still available as they were previously. Users who prefer to use the original interface may still do so by selecting the link entitled Use Classic Interface in the upper-left corner of the screen. For further information about SDA, please select the Getting Started button located in the upper-right portion of the screen.Users no longer need to open the codebook in a separate browser to view a list of variables. Also, users can now switch between the various statistical procedures without having to return to the main analysis page. These improvements are possible because the screen splits into the following four windows:

  1. Program Selection Window. Select from programs to perform analysis, create or recode variables, download the dataset or a customized data subset, view the codebook, or view the help file Getting Started.

  2. Variable Selection Window. The buttons within this window change depending on the type of analysis selected. Variables are selected and placed into the box. The user can then specify which analysis field the variable should go into (i.e., row or column for a crosstabulation, independent or dependent for a regression, or used as a control or filter variable). Users can also obtain a frequency table and accompanying question text for that variable by selecting the View button.

  3. Variable Tree Window. All variables and variable labels are listed and organized as they appear within the codebook, into groups with headings and subheadings. Click on the +/- boxes next to the heading to view all the variables within a selected group. When a variable of interest is located, select it and the program will place it into the variable selection window.

  4. Analysis Window. This screen will display the required and optional fields for the type of analysis you have selected. This screen looks identical to the classic interface for each of the analytic features available.

How do I find a study by Principal Investigator?

Perform a keyword search in the "Study descriptions" tab. Then you can use the "Filter by Author" facet in the right column.

Can I select multiple datasets for a download? What about multiple stat packages?

For every study in the archive you have the option of either downloading all of the files or selecting individual files. Use the option of downloading all files if you want more than one part (dataset) of a multiple part study, or if you want to download the study into multiple statistical packages. There is not a way to "cherry pick" datasets or statistical packages. You cannot select datasets 1 and 3 with a single click. Similarly, you cannot select SAS and Stata, but not SPSS. Once you have downloaded the entire study you can then select which individual files to extract from the zip file provided.

What is SDA and why should I use it?

The Survey Documentation and Analysis (SDA) system allows users to conduct statistical analysis quickly and efficiently on the Internet using their Web browser. It was developed by the Computer-assisted Survey Methods Program (CSM) at the University of California at Berkeley. The SDA system is capable of performing a wide range of statistical analyses from bivariate crosstabulation to multiple regression and analysis of variance. The system allows users to design and implement custom recodes as well as generate subsets of data for download and analysis with traditional statistical applications.

For an overview on how to analyze data online, please consult our SDA Tutorial.

Additional information about SDA and its capabilities can be found in the SDA online documentation from Berkeley.

What is faceted searching? How does it work?

With the new SAMHDA Web site, SAMHDA has enhanced searching our data holdings using SOLR. SOLR offers the following advantages:

  • Faceted searching
  • No more limit of 500 results
  • Date searching of multiple fields
  • Same search rules for data holdings, bibliography, and variables database

Faceted searching alone is a significant improvement.

  • Easy to shift between refining and expanding search results
  • Unlikely to hit "no results found" page as facets provide an indicator of the size of your result set
  • Seamless integration with keyword searching

The SAMHDA site features two types of searches: variables and study descriptions. By default, you search the variables in the studies.

Variables

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In the screen above, I've done a search on "methamphetamine." The results page lists all the studies that have variables on methamphetamine, sorted by the number of matching variables. I'm not sure I want to limit myself to one study just yet, so I'm going to click on "Find matching variables in all studies" atop the page to return a list of all variables.

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This returns nearly 2300 variables, which is a bit more than I want to page through. Looking to the right, I can see several facets for narrowing my results. Since I'm interested in looking at relatively current data, I select "2000-2009" under "Filter by Time Period." You'll note that it provides an indication of how many results I'll find. I've also sorted by "Time Period (newest)" to pull the most current variables to the top of the list.

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Now that I've selected a facet, it no longer appears on the right, and I can see "time period:2000-2009" just above my search results. If I were to click on the "X" next to it, it would re-execute the search, removing that particular term. Thus I can narrow my search quickly by selecting a link to the right, or expand my search by removing a previously selected filter/facet. I can see a really good candidate in the list: "Ever used methamphetamine."

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Clicking on the variable label takes me to a screen with additional information, including the full question text, responses, and frequencies.

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Scrolling further down the page, I can see additional options. The option "view the study home page" will take me to the main entry point for the study, where I can read more on the sample, download the data files (in SAS, SPSS, or Stata format), and perform online analysis.

Study Descriptions

You can also search the study descriptions if you're looking for a particular study, investigator, or agency. If you click on the "Go" button without entering a search term, it automatically returns all studies.

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Thus I can see that SAMHDA has 134 different studies. Looking to the right, I can see more facets, some of which are not available for variables. The subject facet gives a broad description of SAMHDA's holdings in this case. The "more" link expanded the facet from the top 5 terms to the top 15. A "less" link appears if you want to shrink the list again. There's a "view all" link at the bottom of the list, which I'll now follow.

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The "view all" link returns a comprehensive list of all the subject terms assigned to SAMHDA studies, along with a count of how many studies were thus tagged. The book icon enables you to go to the thesaurus entry for that term if you want to find broader, narrower, or related terms, and clicking on the word itself performs a search for that term.

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I've selected "cocaine," which returned 29 results. The subject facet no longer appears, and so other facets have risen to the top. I can use the other facets to narrow my results further by geography, time period, investigator, series, or recency (added to the site).