Strengths and limitations
We undertook a thorough search of the current literature, undergoing
analysis by two independent reviewers with strict quality assessment.
Attempts were made to mitigate inter-study heterogeneity by division of
studies into groups. All index tests are relevant to primary care and
immediately available without novel techniques or additional training.
There were, however, limitations. Due to difficulties in data extraction
from some non-English journals, 15 studies were excluded from the
analysis. Some studies, such as Chapron et al 2005, which was seminal in
providing a clinical prediction model for moderate/severe endometriosis,
were not able to be included due to the inability for construct 2x2
tables.37 We did not contact authors to obtain
individual data that was not available in the published text.
Overall, there was significant methodological variance and population
heterogeneity in age; presentation; and stage of disease. Variation in
selection of cases and controls may not reflect a clinically
representative population. Prevalence of disease was higher than seen in
the general female population, which may reflect a high degree of
surgical accuracy, but also indicates the selective nature of study
populations.
There is the possibility of inappropriate assignment of cases and
controls, occurring in both directions due to uneven application of the
reference standard, although we attempted to account for this by
assigning groups. We included studies that diagnosed endometriosis by
visual inspection and there is debate regarding this in the absence of
histological confirmation.38-40
There was variation in the definition of positive symptom index tests.
This is common across many reviews and although there is guidance on
symptom reporting, it was not clearly followed in all
studies.41-43 Assessment of symptoms varied, with most
studies using a self-administered questionnaire. Although the use of
standardised validated tools would better allow for comparison across
studies, the nuance and detail acquired through clinical history taking
is likely to better grasp the nature and significance of a symptom and
its implications.
It is likely that imaging and surgical techniques have developed over
time. A trend towards recent studies may mitigate this.
Considering the balances of strengths and weaknesses, however, we
believe that our data synthesis presents an objective summary of the
current evidence.