Addressing Quantitative and Qualitative Hypotheses Using Regression Models with Equality Restrictions and Predictors Measured in Common Units.

In regression, some or all of the predictors may be measured in common units: e.g. X1 = carbohydrate calories, X2 = protein calories, X3 = fat calories. Such predictors can occur in disciplines as diverse as business, economics, education, medicine, nutrition, psychology, sport science, etc. Predictors in common units can lead to unique quantitative and qualitative hypotheses that can be addressed by imposing equality restrictions on the regression weights (e.g. b1=b2=b3). A simple device, total score substitution, is available for constraining regression coefficients to be equal in a variety of regression applications. Applications to linear, moderated linear, and polynomial models are described, but extensions to generalized linear models and multilevel linear models are also possible. Total score substitution in linear and moderated regression is illustrated using high school coursework and mathematics achievement data. Data, code (R, SPSS, SAS), and output are publicly available.

Thirty years later: Locating and interviewing participants of the Chicago Longitudinal Study.

Retaining study participants over time is essential for longitudinal studies to prevent selection bias and to achieve their long-term goals. The present paper examines the extent to which participants can be retained in a 30-year longitudinal study when a multi-pronged approach is employed. The paper specifically describes the approach that was used to locate and interview participants of the Chicago Longitudinal Study (CLS), three decades after the study began. The CLS is a prospective cohort investigation that examines the effects of the Child-Parent Center (CPC) program, a school-based intervention for low-income children from preschool through 3rd grade. The original CLS sample included a complete cohort of 1,539 children who were born in low-income areas in 1979-1980 and attended kindergarten in 1985-1986 at Chicago Public Schools. The CLS conducted a follow-up survey when participants were approximately age 35. After relatively slow initial progress, CLS researchers developed a comprehensive strategy to locate and interview participants, including: (a) adoption of detailed, manualized tracking protocol, (b) utilization of multiple search platforms, ranging from public search engines to social media, (c) assistance from state correctional facilities, and (d) neighborhood canvassing and in-person interviews. This tracking and interview process facilitated 735 completed interviews within 27 months, compared to 370 completed interviews in the 32 months prior to the launch of the comprehensive tracking protocol. Altogether, 1,105 interviews were conducted, representing an effective completion rate of 76.5%. Recommendations for strengthening response rates in other longitudinal studies are discussed.