BackgroundEmpirical evidence demonstrates that informal patient payments are an important feature of many health care systems. However, the study of these payments is a challenging task because of their potentially illegal and sensitive nature. The aim of this paper is to provide a systematic review and analysis of key methodological difficulties in measuring informal patient payments.MethodsThe systematic review was based on the following eligibility criteria: English language publications that reported on empirical studies measuring informal patient payments. There were no limitations with regard to the year of publication. The content of the publications was analysed qualitatively and the results were organised in the form of tables. Data sources were Econlit, Econpapers, Medline, PubMed, ScienceDirect, SocINDEX.ResultsInformal payments for health care services are most often investigated in studies involving patients or the general public, but providers and officials are also sample units in some studies. The majority of the studies apply a single mode of data collection that involves either face-to-face interviews or group discussions.One of the main methodological difficulties reported in the publication concerns the inability of some respondents to distinguish between official and unofficial payments. Another complication is associated with the refusal of some respondents to answer questions on informal patient payments.We do not exclude the possibility that we have missed studies that reported in non-English language journals as well as very recent studies that are not yet published.ConclusionsGiven the recent evidence from research on survey methods, a self-administrated questionnaire during a face-to-face interview could be a suitable mode of collecting sensitive data, such as data on informal patient payments.

In this study we aim to compare the public perceptions towards informal patient payments in six Central and Eastern European countries (Bulgaria, Hungary, Lithuania, Poland, Romania and Ukraine). Overall, around 35–60% of the general public in each country has ever made informal payments, though informal cash payments are perceived negatively, mostly as corruption. In-kind gifts are often seen as a token of gratitude. However, significant differences among countries are observed. Despite the public support for the eradication of informal payments, there are population groups who favor their existence and this should be taken into account in policy-making.