**Core Concept**
Qualitative research in medicine involves collecting and analyzing non-numerical data, such as text, images, or observations. This type of research aims to gain a deeper understanding of a phenomenon or experience.

**Why the Correct Answer is Right**
Qualitative data is typically collected using methods like interviews, focus groups, or content analysis. The correct answer is right because it represents a type of data that is not numerical or quantitative. Researchers use qualitative data to identify themes, patterns, and meanings that may not be apparent through quantitative analysis.

**Why Each Wrong Option is Incorrect**
**Option A:** Quantitative data is numerical and can be measured or counted. It is often used in studies that aim to determine the frequency, prevalence, or association between variables.
**Option B:** Mixed-methods research combines both qualitative and quantitative approaches to gain a more comprehensive understanding of a research question. While it may involve qualitative data, it is not exclusive to qualitative data.
**Option C:** The correct answer is missing, but we can assume it's the one that represents qualitative data. If that's the case, this option is incorrect because it's the correct answer, not the distractor.

**Clinical Pearl / High-Yield Fact**
When designing a research study, it's essential to consider the type of data you want to collect and the methods that best suit your research question. Qualitative data is particularly useful for exploring complex phenomena or understanding the experiences of individuals.

**Correct Answer:** D. Qualitative data.