Markus: Your post is s timely one because it picks up on a very active literature in the field of implementation / public administration research that falls under the rubric of "street level bureaucracy". The field worker similar to a front-line worker in a line ministry, are really the only actual contact person encountered by the survey respondent and it is this discretionary power that yields them considerable influence in how the intervention is experienced. The takeaway from the large literature is that these street -level or front-end staff will operate in a fashion that is really beyond the control of senior / head office managers. This does always mean that these workers will work to actively sabotage the aims of objectives but their actions might have this thus unwitting result. Economists have thought about this in terms of the principal agent framework and there is the resulting optimal contracting literature to try and align the differing incentives between the principal ( investigators) and agents ie field workers. Indeed one recommendation is for senior researchers/managers focus their attention on the wording of their employment contracts issued to workers or rather the firms that are typically sub-contracted to collect the data in question. So if there are perverse incentives these could be picked earlier or through improved oversight by reducing task burden or appointing dedicated quality assurance staff person(s). However the takeaway from the street level bureaucracy literature is that such managerial / top down approaches can be expected to have limited success. This is because these workers irrespective of the training or oversight including potential punishment will still use a variety of coping mechanisms to carry out their task and meet set goals given time & resource constraints. For instance one coping mechanism is the use of short cuts such scheduling the visit or appointment at a time inconvenient for the respondent thereby recording a no show . Alternatively the data collector might simply require respondents to show up at community center to minimize effort and thereby collect the information only from those willing and able to attend. Or spending time with the more obliging/ educated respondents to ease data collection. In the case of research from the US social workers assigned to mete out unemployment benefits to single mothers would schedule group appointments so as maximize waiting time for application processing and thereby create a deterrent to mothers unable to wait because of childcare or work obligations! As such it would be important for researchers and managers to spend some time observing how fuels workers are collecting information to understand the type and nature of coping mechanisms used in the course of their duties.