Final answer:
A decrease in the unemployment rate can occur with a proportionately equal decrease in the labor force, as it will result in a lower unemployment rate when the number of unemployed decreases along with the labor force size.
Step-by-step explanation:
The question revolves around the scenarios that can lead to a decrease in the unemployment rate. Option B, which suggests a proportionately equal decrease in the labor force, will cause the unemployment rate to decrease. This is because the unemployment rate is calculated by dividing the number of unemployed individuals by the total labor force. If the labor force shrinks while the number of employed people remains constant, the unemployment rate goes down.
Let's look at an example. Assume there are 100 people in the labor force and 5 are unemployed, making the unemployment rate 5%. If 10 people (including the 5 unemployed) leave the labor force, there would be 90 people left, with none unemployed, thus the unemployment rate drops to 0%.
This situation differs from an increase in population with no change in the labor force (Option A), as the unemployment rate specifies unemployment within the labor force, not the entire population. Similarly, the concept of discouraged workers plays a role in the unemployment rate as they exit the labor force, leading to a misleading drop in the unemployment rate. This can occur because discouraged workers are no longer counted as unemployed once they stop searching for jobs even though the number of working positions remains unchanged or declines.