What factors affect surgical outcomes as identified in the study?

The choice of "variables" in understanding factors that affect surgical outcomes is correct because it encompasses a wide range of influences that can impact the success of a surgical procedure. Variables in this context refer to patient-specific factors such as age, underlying health conditions, and the presence of comorbidities, as well as procedural factors including the type of surgery performed and the skill level of the surgical team.

Each of these variables interacts in complex ways to determine the effectiveness of the surgery and the recovery process. By acknowledging these various factors as "variables," the answer highlights the multifaceted nature of surgical outcomes and framing them in a broad context helps to understand that successful surgical results depend not just on the procedure itself but also on numerous dynamic components surrounding it.

In contrast, other options such as medical equipment, surgical tools, and physical therapy are all relevant to surgical processes but fall into specific categories or aspects rather than representing the diverse range of patient and procedure-related influences collected under the term "variables." Thus, the emphasis on "variables" captures the holistic view necessary for evaluating surgical outcomes.