What is the prevalence of honorary or ghost authorship in leading medical journals?

Was it easy to reach a judgment regarding your overall confidence in the results of each review (i.e. high/moderate/low/critically low) using AMSTAR2?

If not, why not? Were there any specific items you struggled with?

Could you complete the assessment alone and without reference to any other documents, i.e. those not provided with the tool? If not, why not?