The business requirement is to count the number of unique rodents that have participated in at least one maze experiment. The MazeEscapes table serves as a fact table, recording every attempt. A single rodent can have multiple entries in this table. Therefore, to find the number of unique rodents who have made attempts, we must count the distinct RodentID values present in the MazeEscapes table. The expression Count(Distinct RodentID) correctly performs this aggregation, counting each rodent only once, regardless of how many attempts they have made.

B: This calculates the total number of rodents in the master Rodent table, not the number of rodents who have actually attempted a maze.

C: This calculates the total number of maze attempts by summing a '1' for each row in the MazeEscapes table, not the number of unique rodents.

D: This also calculates the total number of rodents in the master Rodent table, which is not what the business analyst needs to measure.

1. Qlik Sense for Windows Help, Count - chart function: The official documentation specifies the use of the distinct qualifier. It states, "If the word distinct occurs before the expression, all duplicates are disregarded." This directly supports using Count(Distinct RodentID) to find the number of unique participants.

Source: Qlik Sense on Windows Help, Document ID: QlikSenseonWindowsMay2024, Section: Visualizations > Expressions > Chart functions > Aggregation functions > Count - chart function.

2. Qlik Sense for Windows Help, Best practices for data modeling: This documentation explains the fundamental concept of fact and dimension tables. The MazeEscapes table is a transactional (fact) table, and the Rodent table is a dimensional (master data) table. To analyze events or transactions (like maze attempts), aggregations must be performed on the fact table. This principle invalidates options B and D, which incorrectly query the dimension table for this specific KPI.

Source: Qlik Sense on Windows Help, Document ID: QlikSenseonWindowsMay2024, Section: Preparing data > Best practices for data modeling > Star schema.

3. Qlik Sense for Windows Help, KPI: The documentation on creating KPIs shows that the primary component is the "Measure," which is defined by an expression. The expression Count(Distinct RodentID) is a valid measure for a KPI object designed to show a single, key performance indicator like the number of active rodents.

Source: Qlik Sense on Windows Help, Document ID: QlikSenseonWindowsMay2024, Section: Visualizations > KPI > Properties > Data > Measures.