Good question Mehmet. I would imagine that the Kinshuk et al findings might represent a certain type of 'stereo-type'. Single author articles can be viewed with suspicion i.e. clinical trials - and would either not be published or not well cited. Single authors may also be inexperienced authors - and the product not always highly citable. On the other hand, single authors may well be highly experienced authors who are/have produced seminal work - and they are highly cited because of their established reputation. I would imagine this finding is highly variable

In a general perspective, scientific research articles perceived as structured, organized, integrated modules. In order to achieve this kind of integrity one author (with a natural integrity or natural integrated cognition) may be more appropriate than multiple authors (with multiple cognition or naturally different perspectives).