Several proposals to establish a quality of life (QOL) index were investigated by ______________.

The correct answer is Hornback, as this individual has been recognized for their contributions and investigations related to the establishment of a quality of life (QOL) index. Hornback's work typically involves analyzing various factors that influence community wellbeing and designing indexes that reflect those multifaceted aspects. This includes evaluating economic, social, environmental, and health-related parameters that together define quality of life within different populations or regions.

In the context of developing a QOL index, it is essential to have an authoritative figure or researcher whose work aligns with understanding and measuring these complex interactions. The research process often entails gathering data, analyzing existing conditions, and proposing frameworks to quantify quality of life, which is a significant endeavor in environmental health, urban planning, and policy-making.

Other names mentioned do not have the same recognition or contribution in this area, underscoring Hornback’s specific relevance to the topic of QOL indexes.