Without access to the specific chart referenced, we can analyze the options based on typical data monitoring practices for Average Length of Stay (ALOS) in patients with Acute Myocardial Infarction (AMI).

Option A: "Data collection should be continued for an additional quarter."

Continuous data collection is a standard practice in healthcare quality management to monitor trends over time. However, this option does not provide a specific conclusion about the current data.

Option B: "The average length of stay is consistent with the national average."

To conclude this, a comparison between the hospital's ALOS data and national benchmarks is necessary. Without such comparative data, this conclusion cannot be drawn.

Option C: "The average length of stay is highest during the fourth quarter."

If the chart indicates a peak in ALOS during the fourth quarter, this conclusion is directly supported by the data. Identifying such seasonal variations is crucial for resource planning and quality improvement initiatives.

Option D: "Standard deviation is needed to determine the degree of control."

Standard deviation is a statistical measure that quantifies the amount of variation or dispersion in a set of data values. While calculating standard deviation can provide insights into data variability, it is not a conclusion but rather an analytical step.

Therefore, based on the typical interpretation of such data, Option C is the most appropriate conclusion, assuming the chart shows an increase in ALOS during the fourth quarter.