**Core Concept**
The investigator is categorizing patients based on their HIV status, which is a binary variable (HIV-positive or HIV-negative). This type of data is used to compare outcomes between two distinct groups.

**Why the Correct Answer is Right**
This division constitutes a type of data known as **categorical data** or **nominal data**. Categorical data is used to classify individuals or observations into distinct categories, which in this case are HIV-positive and HIV-negative. This type of data is often used in epidemiological studies to compare outcomes between different groups.

**Why Each Wrong Option is Incorrect**
**Option A:** Continuous data refers to numerical data that can take on any value within a given range, such as height or weight. This is not the case in this scenario, where patients are categorized into two distinct groups.

**Option B:** Ordinal data is a type of categorical data where the categories have a natural order or ranking, such as disease severity or educational level. However, in this case, the categories are simply HIV-positive or HIV-negative, without any inherent order.

**Option C:** Ratio data is a type of numerical data where the zero point is meaningful, such as temperature or blood pressure. This is not relevant to the scenario, where patients are categorized into two groups based on their HIV status.

**Clinical Pearl / High-Yield Fact**
When analyzing data, it's essential to determine the type of data being collected to choose the appropriate statistical analysis methods.

**Correct Answer:** B. Categorical data.