The expansive profession of ghostwriting can trace its roots back to several centuries, though it has evolved and flourished tremendously in the last few decades. In essence, ghostwriters are professional writers hired to draft and polish various types of content while maintaining confidentiality and allowing their clients to take credit for the work. Ghostwriters are employed across various sectors including literature, music, and scriptwriting, but the primary focus of this discussion will be the literary ghostwriting sphere in the United States.

Delving into the statistical analysis, the ghostwriting industry in the U.S. is a multi-billion dollar business, with thousands of ghostwriters working across the country. Despite the size of the industry, there is a surprising dearth of data. Much of this can be attributed to the clandestine nature of the profession, as the raison d'être of a ghostwriter is to remain invisible. However, we can glean some insights from various sources including literary agencies, publishing companies, and anonymous surveys.

Economically, it is challenging to estimate the exact value of the U.S. ghostwriting industry due to the secrecy surrounding individual project fees and the broad range of the projects' scope. Nevertheless, reports suggest that experienced ghostwriters can charge anywhere from $25,000 to $100,000 per project, with those at the higher end of the spectrum having a strong portfolio or a niche expertise.

From a legal perspective, ghostwriting raises intriguing questions regarding intellectual property rights. A ghostwriter usually forgoes any legal claim to the work, with the copyright typically belonging to the person or entity that commissioned the work. Nonetheless, the exact terms can vary, and are usually established in a formal agreement between the ghostwriter and the client.

In terms of techniques employed by ghostwriters, the process often involves a comprehensive understanding of the client's voice, style, and viewpoint. This requires substantial research and collaboration. More often than not, ghostwriters are adept at adapting their writing style to match their client's voice convincingly. They use various software tools to improve the efficiency and quality of their work. From sophisticated language processing algorithms to plagiarism checkers, technology has become an indispensable part of a ghostwriter's arsenal.

The demand for ghostwriting services has seen a significant and steady increase over the past few years, primarily attributed to the rise of self-publishing and content marketing. Today, ghostwriters are being hired not just by celebrities and politicians, but also by business leaders, professionals, and even everyday people who wish to share their stories but lack the time or the writing expertise.

In a speculative vein, the future of the U.S. ghostwriting industry looks promising. As the digital age continues to thrive, the demand for high-quality, original content is set to surge. And with it, the need for skilled ghostwriters who can meet this demand while seamlessly embodying their client's voice will also rise.

In conclusion, the U.S. ghostwriting industry, veiled in mystery and secrecy, is a vibrant and thriving field. It offers a fascinating exploration into the evolving landscape of authorship, where the brilliance of anonymity and the subtlety of voice adaptation come together. And while capturing concrete data may prove challenging due to the industry's very nature, one thing is clear - the ghostwriting profession is an integral part of the literary world and its significance cannot be understated.