Just from the abstract I can't tell if the study differentiates between sole proprietorship and solo founders. The former is a business built around a person's individual skill set. The latter is built around an idea, a product, or a service that just happened to be started by a single person. The death test can differentiate: a sole proprietorship goes out of business if the founder dies. A company created by a solo entrepreneur will continue to operate and serve customers even if the founder passes away.

Investors may favor partnerships over solo ventures due to the proprietorship effect. A skills-based solo founder is usually too idiomatic to be an investable business. The catch here is when starting out a solo founder must be a sole proprietor; it's his particular skillset and drive that creates the company. The trap is it's natural for the business to evolve and grow around that particular skillset.