Monitoring the Future: A Continuing Study of American Youth (8th- and 10th-Grade Surveys), 2014 (ICPSR 36149)

1. This study was conducted by the Survey Research Center, Institute for Social Research at the University of Michigan.

2. Subsequent to a significant change made in 2012, the data files from the two grades and four forms are merged to create a single file. The variables V3 and V501 designate the form number and grade, respectively. The end of each variable label lists the form(s) on which the question appeared. The missing value (-8) is used to distinguish those cases where the question corresponding to a given variable was not asked on a particular form.

3. To protect the anonymity of respondents, all variables that could be used to identify individuals have been collapsed or recoded in the public use files. These modifications should not affect analytic uses of the public use files.

4. Variables omitted from the Western region questionnaires are noted in the codebook.

5. A user guide is provided with the study documentation. It contains a cross-time question index for the MTF 8th- and 10th-grade surveys. The document is sorted by subject area.

6. Frequency and percentage distributions displayed in the 2014 codebook are unweighted.

7. MTF does not release detailed geography codes in its public use files because of the disclosure risk it would cause. The MTF sample is drawn to generate representative samples of the four Census Bureau regions of the country (Northeast, Midwest, South, and West), but it does not generate representative samples of smaller geographic areas such as states, counties, or cities. For additional information about data that is withheld from the public use files please contact MTF directly at mtfinformation@umich.edu.

8. With the approval of the MTF Principal Investigators ICPSR created a series of dichotomous recodes for 10 substances for the three standard time periods (lifetime, past 12 months, and past 30 days). The substances include tobacco, alcohol, marijuana, LSD, other psychedelics, amphetamines, sedatives/barbiturates, tranquilizers, inhalants, and other narcotics. These variables have been placed at the end of the data file. Each variable has the same name and label as the original, but with the addition of the letter "D" at the end of the variable name and the words "(dichotomous recode)" included at the end of the variable label.

9. Using these new dichotomous recode variables ICPSR has created interactive maps to show the weighted response for each dichotomous variable by Census region. To create a map simply select the desired year/grade and question/variable. Then click on "Go". The resulting map will rank the regions by color. The Census region with the darkest shade will show the highest frequency of use. A frequency table is also provided.

• Johnston, Lloyd D., Jerald G. Bachman, Patrick M. O'Malley, John E. Schulenberg, and Richard A Miech. Monitoring the Future: A Continuing Study of American Youth (8th- and 10th-Grade Surveys), 2014. ICPSR36149-v1. Ann Arbor, MI: Inter-university Consortium for Political and Social Research [distributor], 2015-10-26. http://doi.org/10.3886/ICPSR36149.v1

2015-10-26 ICPSR data undergo a confidentiality review and are altered when necessary to limit the risk of disclosure. ICPSR also routinely creates ready-to-go data files along with setups in the major statistical software formats as well as standard codebooks to accompany the data. In addition to these procedures, ICPSR performed the following processing steps for this data collection:

• Standardized missing values.
• Created online analysis version with question text.
• Performed recodes and/or calculated derived variables.
• Checked for undocumented or out-of-range codes.