Data used to assess the efficiency and effectiveness of health care services provided to an individual or group of individuals is:

The correct choice highlights that data specifically linked to individual patients—often referred to as patient identifiable data—play a crucial role in assessing the efficiency and effectiveness of healthcare services. Such data can include personal health information, treatment records, and clinical outcomes related to specific patients. By analyzing this kind of data, healthcare providers can gain insights into how well services are being delivered to individual patients, identify areas for improvement, and tailor interventions to enhance patient care quality.

In contrast, aggregate data refers to information that has been compiled from multiple patients and is often used for broader analyses rather than assessing individual care. This data helps in understanding trends and patterns in healthcare but does not provide insights specific to individual patient experiences.

De-identified data has had all personally identifiable information removed to protect patient privacy. While useful for research and analysis, it doesn't allow for an examination of services at the level of individual patients. Lastly, population-based data considers health outcomes and services across larger groups, such as communities or demographics, which can be valuable for public health assessments but doesn’t focus on the individual patient level.