A few companies will refer to their JREs as REs - ie Research Executive will be the first title you get. We tend to use 'RE' for positions requiring around 1-3 years' experience, with descriptions suggesting a lot of basic learning still going on and close supervision - however REs are right in the thick of it and will be expected to plough through a lot of the meaty work of the agency, from planning analysis to supervising fieldwork, accompanying their Directors to meet clients (JREs do this too) and trying their hand at presenting, albeit generally parts of presentations or relatively tame audiences.
Generally speaking REs as we define them will not get involved in business development, will not be presenting to key clients and are unlikely to have much input to proposals, unless it's researching background material for a more senior person to write up. They are likely to be briefing interviewers, where traditional fieldwork is involved; conducting interviews and in some cases running group discussions themselves. With newer types of project, they will still be tracking the progress of data collection and spotting or trying to pre-empt problems, 'though they might be data feeds or dashboards; or they might be helping to monitor and engage online communities. REs will act as everyday contacts for clients in some cases, but obviously with more supervision and likelihood to escalate than with SREs.
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