The Twins and Siblings study is available in a machine-readable data file that is part of the High School and Beyond (HSB) Class of 1980 Survey, administered in 1980 to a national sample of over 30,000 sophomores and 28,000 seniors from 1,015 high schools throughout the United States. This file contains data from 616 sampled twins and triplets with augmented data for 461 twins and triplets of survey-sampled members and 1,641 responses of non-twin siblings, all of whom are identified in the HSB base-year survey. The file consists of 2,718 records (students) representing 1,348 separate families. It contains all of the variables on the HSB student file plus family identification number and type of twin or sibling. Data for both sophomores and seniors include personal background, school activities, out-of-school activities, attitudes, and post-high school plans and aspirations. Cognitive test data for sophomores include: (1) vocabulary; (2) reading; (3) mathematics; (4) science; (5) writing; and (6) civics education. Data for seniors include cognitive test data on: (1) vocabulary; (2) mathematics; (3) picture numbers; (4) mosaic comparisons; and (5) visualization in three dimensions. The 121 questions of the senior questionnaire and the 114 of the sophomore questionnaire included 89 questions in common. The file includes information on a total of 640 variables of family structure and finances. TYPE OF SURVEY: National Survey; Sample Survey. POPULATION: Sophomores and Seniors in the HSB Study with Twin and Triplet Siblings (642 Sets); Sophomores and Seniors in the HSB Study with Non-Twin Siblings (840 Sets). SAMPLE: HSB Sophomore and Senior Twins and Triplets (538 Sets); HSB Sophomore and Senior Non-Twin Siblings (824 Sets). RESPONDENTS: HSB Sophomore and Senior Twins and Triplets (524 Sets); HSB Sophomore and Senior Non-Twin Siblings (810 Sets); Both (14 Sets). RESPONSE RATE: HSB Sophomore and Senior Twins and Triplets (97.4%); HSB Sophomore and Senior Non-Twin Siblings (98.4%). FREQUENCY: Once. YEAR OF EARLIEST DATA: 1980. YEAR OF LATEST DATA: 1980. (SLD)