Cost of obtaining an output value Different means of obtaining an output
value come at different costs. Implicit strategies, such as treating a user click
on a suggested item as positive output, or not clicking as negative, are inexpensive in relation to user effort. Conversely, asking the user to explicitly rate
an item is more costly, though still dependent on the task. Watching a movie
like Star Wars to rate may provide good results but requires substantial user
effort [20]; rating a joke requires much less. This often dovetails the exploration/exploitation coupling and trade-offs between obtaining outputs from
different inputs should also be considered (e.g. certainty/uncertainty, ease of
evaluation, etc.)