A study compiles and analyzes observational data from multiple patients without a control group. What type of study is this?

A case series is a descriptive observational study that documents characteristics, clinical findings, or outcomes of a group of patients with similar conditions. It lacks a control group, randomization, and hypothesis testing. Case series are valuable for describing rare conditions, new disease presentations, or complications of treatments. They generate hypotheses but cannot establish causation. Examples in dentistry include early reports of bisphosphonate-related osteonecrosis and initial descriptions of oral manifestations of HIV. Note: This question is conceptually related to Q90 but uses slightly different wording.