It has been shown in a wide variety of studies that treatment in the framework of research studies has advantages for patients — partly because more intensive clinical care and monitoring is provided, and also because there are positive psychological effects involving better coping with the disease and the ability to receive the latest innovative therapies [3]. In addition, research studies lead to increased knowledge about the pathogenesis and risk factors in diseases [6]. In a questionnaire study conducted among American oncologists by Somkin et al. in 2005, 67 % of the physicians stated that the treatment of patients in clinical studies was always the treatment of choice [7]. Despite this, recruitment rates of research studies are well below 10 % in many certified centers [8]. The study recruitment rate for all certified German breast cancer centers in 2012 showed a median of 11.3 % [9]. It is therefore clearly necessary to optimize recruitment strategies. These strategies should be based on the patients’ attitudes and knowledge about clinical studies.

The present study shows that patients are on average “moderately well-informed” in relation to clinical studies, according to a score based on four questions used as a separate indicator of existing knowledge about clinical studies — i.e., the patients answered an average of 2.06 questions correctly. Middle-aged patients, those with a high educational level, and those presenting with pregnancy or endometriosis had the best levels of information about studies.

A report from Australia calculated a knowledge score on the topic of clinical studies among 50 outpatient internal medicine/oncology patients [5]. The findings showed that 51.0 % of the patients agreed with the statement that a clinical study discovers whether one method works better than another. A systematic review and meta-analysis included 103 studies analyzing patients’ knowledge about different aspects of clinical trials. The pooled percentage of participants was 62.9 % for knowing that treatments were being compared [10]. In comparison, 83.7 % of the patients in the present study agreed that this statement was true. By contrast, 74.0 % of the Australian group were certain that the physician treating them would ensure that a patient taking part in a study would receive the best possible treatment — whereas in the present study only 47.8 % agreed with this. There was a correspondence in relation to the statement that clinical studies are only used when the situation is hopeless (18.0 % versus 18.5 %). The view that clinical studies test procedures etc. that no one is yet certain about was agreed to by only 19.0 % in the Australian group, in comparison with 51.5 % of the patients in the present study. Evidently, patients in the present group were much more uncertain in relation to the individual questions listed. Both questionnaires used the knowledge rating scale tool. Studies have identified a positive connection between patients’ willingness to participate and the number of correct answers regarding knowledge about clinical studies [8, 11]. By comparison, the median score in the present group was two (out of four key questions), with the average lying at 51.5 %, while in Australia it was three out of seven questions. The meta-analysis showed that the proportion of participants who understood different components of clinical trials varied from 52.1 % to 75.8 % [10].

Bergenmar and colleagues have factors associated with patients’ knowledge and perceived understanding of clinical trials by using a knowledge score test in 268 patients who consented to participate in a clinical trial [12]. No significant associations were found between knowledge and clinical and socio-economic factors. In contrast to these findings, the present study shows significant influences relative to age, presenting condition, and educational level; this may be explained by the larger number of participants and a better ability to detect statistical differences. The positive influence of lower age and higher education on knowledge has been confirmed by other studies [11].

Research studies were considered useful by 91.6 % of the patients, but only 52.8 % were actually willing to take part in studies themselves. The discrepancy between general approval of clinical studies and patients’ actual or real willingness to take part in them has also been reported in other studies [8, 13, 14]. Ellis et al. reported that women who were willing to consider taking part in a randomized trial were younger and had a higher educational level [8]. Both of these aspects were confirmed by the present study, but there was also a group of very young women who showed less willingness to participate.

A patient’s decision on whether to take part in a study is influenced more by the potential disadvantages than by the potential advantages [14]. The majority of the respondents have a negative image of clinical studies and of the potential disadvantages [14, 15]. Frequently mentioned reasons for not taking part in studies include, for example, a fear of being used as a guinea-pig [8], the increased personal effort involved [8, 16], and increased personal risk [16]. Positive reasons for taking part in studies that are mentioned often include making a contribution to scientific progress [13, 17], the hope that one will receive what is currently the best form of treatment [8] or better treatment and care in comparison with the standard therapy [18], and benefits for future generations [8, 13]. The present study shows that a total of 37.1 % of the patients considered that future generations would be likely to benefit most from their participation in a study; by contrast, only 26.9 % thought that they might benefit most as patients themselves.With regard to external influencing factors, it has been shown that recommendations by independent information services often have a positive effect on willingness to participate in studies [5, 8]. This effect was only moderate in the present group, with only one in three patients being positively influenced by this.

Financial incentives only influenced around one in 10 patients in this group in their decision for or against taking part in studies. Reasons for the particularly positive reaction to a financial bonus among women receiving fertility treatment (21.9 %) are likely to be the high costs of this form of treatment and the high level of the excess charge for it that is not met by health insurance companies. Younger patients were also more often influenced by financial remuneration. This may be explained by the general financial burdens faced by younger people (e.g., relative to starting out on their careers, obtaining mortgages for houses, and caring for children).

The great majority of the present group of patients wanted to make the decision about whether or not to participate in a study after consultation with the physician treating them — but nevertheless independently. This finding is also reflected in other studies [5, 15]. Women who have an active decision-making style are more likely to take part in studies than women with a passive decision-making style [8]. Satisfaction with decision-making and subjective informed consent is strongly associated with fewer regrets about decisions [19].

The amount of information desired by patients is also important in the context of autonomy when participating in a study. The majority of patients in the present group (95.9 %) wanted to receive all of the available information during the consultation process. A similar picture has also been described in other studies [5, 15]. Patients who do not believe that they have fully understood the implications of a study may ultimately feel regret about their decision to participate [19].

Altruistic motivations generally play an important role in study participation, as has often been shown in other studies [20, 21]. In addition, the idea that there may be benefits for future patients is associated with high levels of knowledge [22]. Verheggen et al. found that altruistic motives weakened the expected risks of study participation and led to the extra time involved being seen as less burdensome, which in turn led to higher participation rates [16]. In the present group, benefits for the participating patient were regarded as being only secondary; this may be due to the supposed risks and disadvantages of potential participation in a study. This attitude has also been observed in other studies [14]. Although having an altruistic attitude is positively associated with an individual’s potential participation in research studies, it is not a reliable predictive factor [8]. It is only when a benefit for study participants themselves is seen that study participation becomes probable [13, 23].

These findings — both from the current study and also from the numerous other studies cited here — offer some points of departure for optimizing study planning, study design, patient recruitment, and also the conduct of research studies and processing of the results. To begin with, the way in which information is communicated to patients should be optimized — e.g., through early provision of information brochures, posters, etc., in order to dispel incorrect ideas and thus reduce or prevent anxieties [5, 10]. Presentations using audiovisual media can have positive effects on the quality of information and may increase willingness to participate, but evidence on this is still weak and further research is necessary [24].

In addition, the personal relationship of trust between the physician and the study participant, as well as the availability of personal discussions, should be emphasized [25]. The specialist physician treating the patient was the preferred contact person in the present group (81.3 %) for providing information about a study. A sensitive informed consent discussion strengthens the physician–patient relationship, and a positive relationship is regarded as a predictive factor for participation in research studies [26]. Training programs for physicians to help develop special communication skills can lead to more positive attitudes to clinical trials on the part of patients [27].

Involvement of patients’ family physicians would also be an important way of contacting patients in connection with participation in research studies. It is also important to estimate the financial and time pressure involved for study participants and to provide support when appropriate. This might take the form of financial grants for travel costs or treatment costs, for example [28].

The present study has limitations connected with the composition of the study group, with a wide variety of subgroups. There was also a wide range of responses for each question with regard to the assessment of the patients’ level of knowledge about the design and conduct of studies. One reason for this may have been the comprehensibility of some of the questions. There were no defined subgroups that failed to respond to all of the questions. A further limitation of the present study is the reliability and validity of the instruments used. Although the knowledge scale has been used in earlier studies [5] and differences between results can be discussed on a reliable basis, the questionnaire itself was designed for this study and validation is still lacking. On the other hand, the comprehensibility of the questionnaire was checked using interviews with the first 20 participants. Despite this, the overall group was very large, compensating at least in part for the limitations mentioned. Another limitation is the fact that this study only included female participants; however, other studies have not identified any differences, or only minor differences, between male and female participants [12, 22, 29].