**Core Concept**
Diagrams used to display the distribution of qualitative data are essential in medical research and statistics. These diagrams help in visualizing the frequency and percentage of different categories or groups within a dataset, enabling researchers to make informed decisions and draw meaningful conclusions.

**Why the Correct Answer is Right**
Pie charts are a type of diagram used to show the percentage breakdowns for qualitative data. They consist of a circle divided into sectors, with each sector representing a category or group. The size of each sector is proportional to the percentage of the total data it represents. This allows for a quick and easy comparison of the relative frequencies of different categories. In medical research, pie charts are often used to display the results of surveys, patient demographics, or the distribution of disease symptoms.

**Why Each Wrong Option is Incorrect**
**Option A:** Bar charts are used to compare categorical data across different groups, but they are not typically used to show percentage breakdowns for qualitative data.
**Option B:** Histograms are used to display the distribution of continuous data, not qualitative data.
**Option C:** Scatter plots are used to show the relationship between two continuous variables, not to display percentage breakdowns for qualitative data.

**Clinical Pearl / High-Yield Fact**
When using pie charts to display qualitative data, it's essential to ensure that the categories or groups are mutually exclusive and exhaustive, meaning that every data point belongs to exactly one category and all possible categories are represented.

**Correct Answer: C. Histograms are used to display the distribution of continuous data, not qualitative data.