The prevalence of misconduct is difficult to determine. Various surveys have tried to do this with conflicting results, probably because different methods and different definitions of misconduct were used. For example, asking researchers directly whether they have committed misconduct might not give accurate results. Similarly, we do not know how much misconduct goes undetected.
Daniele Fanelli has tried to answer this question in a systematic review of published studies (screening 3207 papers). He combined the results of 18 studies in a meta-analysis. He only included surveys of fabrication or falsification NOT plagiarism.
Fanelli, D. How many scientists fabricate and falsify research? A systematic review and meta-analysis of survey data. PLoS ONE 2009;4(5): e5738. https:doi.org/10.1371/journal.pone.0005738
Estimate the percentage of researchers you think admitted to publication misconduct.