What does it indicate when an outcome measure has been shown to be reliable?

When an outcome measure has been shown to be reliable, it indicates that the measure consistently produces the same results under the same conditions. This consistency is crucial for the measure to be useful across different contexts and populations. Reliability suggests that if a measurement technique is applied to various groups with similar characteristics, it will yield comparable results. Therefore, a reliable measure is beneficial in a variety of populations as it ensures that the findings are valid and can be generalized across different demographics or conditions.

In contrast, the other options do not accurately reflect the implications of reliability. Options relating to expense, applicability to only one population, or subjectivity do not derive from the concept of reliability but rather pertain to other aspects of measurement tools and their applications.