Final answer:
The most effective measure to gauge the success of a customer service intervention is specific numerical ratings on a customer satisfaction survey, as it provides direct and quantifiable feedback from customers.
Step-by-step explanation:
The most effective measure of an intervention designed to improve customer service would likely be specific numerical ratings on a customer satisfaction survey. While the number of customer complaint calls handled per hour may indicate efficiency in addressing issues, it does not directly measure the quality of service. Similarly, customer anecdotes can be informative but may not represent the broader customer experience and are subject to selection bias. Proportion of employees who have completed customer service training shows an investment in improvement, but it is not a direct outcome measure. Specific numerical ratings reflect direct customer feedback and can be aggregated to provide a quantitative measure of service quality.
It is important to consider the context, as demonstrated by Gavi's Fast Food Restaurant, where an intervention to clarify the payment line process succeeded in reducing complaints and stress for clerks. This matches the results of the Arthur et al. (2003) study, supporting the idea that organizational training and subsequent behavioral measurements, tied to customer outcomes, are effective indicators of successful customer service.