Check out my Harvard Dataverse page. I will consistently post new twin study data here.

OpenMx script for twin modeling (coming soon).

This is an ongoing collaborative effort to list secondary data resources for students.

Video tutorials for modeling twin data in OpenMx (coming soon).

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Roper's iPoll allows you to search thousands of variables/questions.

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Ohio Statistics

U.S. Census - Community Facts
Public Health Data Warehouse
Public School Report Card
Crime Data
Traffic Data and Maps

Statistics/Methods:

UCLA IDRE (Stata) (SPSS) (R)
Amazon Mechanical Turk
Multiple Imputation
Hayes' SPSS Macros
Google Search Trends

Other Data Resources:

U.S. Census Bureau 
Panel Study of Income Dynamics
Global Voter Turnout
The World Bank
Child Health