Data collection
For hosting the internet survey and data collection, we used Sawtooth
Software’s (Orem, UT) SSI Web. As recommended by earlier studies, the
identification and selection of the final attributes and levels was
based on literature review, qualitative research and an expert panel
(19) (20) (21). The four stages as described by Heller et al were
applied although we slightly customized these as seen in Figure 1, which
means that we used several data sources in stage 1. To find out which
attributes were important for DE patients, we firstly (Stage 1)
collected data by performing a literature- and qualitative study. We
performed a survey among 28 patients, one focus group with eight
patients prior to their decision making (22) and a focus group with 10
gynaecologists with expertise on deep endometriosis. The results
combined from stage 1 resulted in 158 attributes.
The second step (Stage 2) in attribute development is data reduction.
This was achieved by frequency and rank order by the researchers (JeM
and JS) combined with thematic analysis (grouping attributes with more
or less the same theme), which resulted in 28 attributes. In the third
and fourth stage, concerning respectively removing inappropriate
attributes and wording of attributes, we selected attributes which
comply with the research question, are relevant for the DE population,
and are intelligible for all patients (23). The last process of
attribute selection was performed in collaboration with all members of
the research group, which resulted in eight final attributes (Table 1).
The first part of the survey included questions about baseline
characteristics (i.e. age, educational level, medication use, medical
history and pain symptoms), surgical fear measured with the validated
Dutch surgical fear questionnaire (SFQ) (24) and three health literacy
screening questions. We included the short surgical fear questionnaire,
while we hypothesized that the fear for surgery could influence the
results of the DCE. Women with surgical fear could have a tendency
towards choosing the conservative treatment compared to women with less
surgical fear. The surgical fear has a subscale sum score for short -and
long term fear that ranges from 0 (no fear) to 40 (very afraid), the
total sum score ranges from 0 (no fear) to 80 (very afraid). Pain was
recorded on a numeric rating scale, patients rated their pain intensity
(0 = no pain and 10 = maximum pain, or inapplicable option). The pain
intensity score was obtained for menstrual cycle and non-cycle related
pain, on the dimensions of dysmenorrhea, pelvic pain, dyspareunia,
dysuria and dyschezia.
Part two of this survey included information about the DCE
(Supplementary table S2 includes the attributes explanation). Prior to
the DCE, we asked the women to rank the eight attributes from most
important (1) to least important (8) when making a treatment decision.
In the ranking we did not distinguish between conservative or surgical
treatment. To get familiar with the concept of a DCE, a simple DCE
question for choosing a phone. Subsequently, the actual DCE was
presented with 10 choice sets. Each choice set consisted of two
hypothetical treatment options labeled as pharmaceutical (conservative)
and surgical treatment. The reason for choosing a labeled DCE is that
both conservative and surgical treatment have a number of specific
attributes and levels that are not generic for both treatments. The
women were asked to choose their preferred treatment of choice for each
of the 10 choice sets (Figure 2). The conservative treatment option
included specific attributes like side effects of hormonal treatment:
depressive feelings and the chance of developing osteoporosis. The
surgical option included treatment specific risks like, the chance of
getting a temporary stoma and the chance of permanent intestinal
symptoms (LARS) ( Table 1).