Findings from Econsultancy and Google Analytics suggest the majority of marketers worldwide failed to use attribution models that properly describe the influence of each ad format and marketing channel on the consumer’s purchase path.
The last-click attribution model was the most common method used by marketers and agencies worldwide. Under this model, the last click receives full credit for any revenue generated.
Lesser used methods of attribution—including first-click, the direct counter to last-click; linear, a model that assigns equal weighting to all interactions; and customized by channel, a type of linear model in which marketers assign their own custom value to each touchpoint—were used by a greater number of agencies than marketers.
First-click and last-click attribution models are easiest to measure, but their use can over- or under-credit an ad format’s influence on conversion activity.
I encourage you to read the full article on eMarketer.