Transparency International's Global Corruption Barometer measures the percentage of users of a service who have bribed at least once in the past year to obtain that service in over 100 countries (varies by year); Transparencia Mexicana's Índice Nacional de Corrupción y Buen Gobierno purportedly measures the percentage of times a service was used that involved a bribe (number of bribes/number of times the respondent used the service) for 35 public services in Mexico (but I can't find the question in the questionnaire that asks how many times the service was used). What other sources are available, either internationally or nationally?