Choi et al.: OBSTETRICAL POSTDURAL PUNCTURE HEADACHE STUDIES
55
ologists who have evaluated anesthesia studies.22,23
Similarly, the results of these studies were infrequent-
ly generalizable. Issues with bias and confounding
were also poorly addressed.
Based on these observations, we would suggest the
following changes to improve quality of observational
studies in this field:
The type of studies published in each topic was also
revealing. Optimally, the incidence and clinical course
of PDPH would be examined using prospective fol-
low-up of cohorts (with survival-type analysis for the
latter topic) and interventions for prevention and
treatment would be studied using RCTs. A survey of
the literature indicates that the optimal study designs
for incidence, clinical course, and treatment were
infrequently utilized. Prevention of PDPH was an
exception with the majority of studies being RCTs.
This observation highlights a problem in the practice
of evidence-based medicine with respect to PDPH.
Already, the clinician is faced with a hurdle: most of
the available information upon which reliance is
placed for evidence-based decision making regarding
PDPH is not optimal in the study design.
Attempts to minimize language bias were made by
including citations of all languages although it is pos-
sible that relevant citations not published in English
may have been missed using the described search strat-
egy. Few citations were published in other languages.
Nearly one-fifth of the citations in our database
contained duplicate data. Most of the duplicates
involved abstracts that were subsequently published as
full papers. Of the 67 abstracts, 12 were eventually
found as full papers. These observations raise an inter-
esting dilemma. Meeting abstracts are often the earli-
est reports of studies and can contain important
information,1 7especially since only half of all abstracts
are published in full.18,19 However, the peer review
process may be less stringent than for full manuscripts
and the quality of abstracts may be low.2 0 As well, the
findings of abstracts may differ drastically from the
subsequent papers. In a subset of obstetrical anesthe-
sia abstracts, Halpern et al. found a large number of
discrepancies between the abstracts and the full
papers.2 1 The choice to include or exclude abstracts
remains controversial.
1. Subjects should be representative of the entire
population of potential participants.
2. Where possible, patients of different cohorts (for
cohort studies) or cases and controls (for case-control
studies) should be recruited from the same population
over the same time period to minimize confounders
relating to population and time.
3. Where possible, subjects and individuals measur-
ing the outcomes should be blinded. The same indi-
viduals should measure all groups.
4. Patient characteristics, possible confounders,
interventions, and all relevant outcomes and adverse
effects should be reported clearly. A flow diagram may
assist the reader in tracking the fate of patients.
5. Follow-up should be reported along with a
description of patients who withdraw or are lost to fol-
low-up.
6. Analyses need to adjust for confounders and time
factors.
7. Power analysis should be performed to ensure an
adequate sample size for the effect that one wishes to
detect. The analysis should be reported.
The weaknesses observed in the RCTs in MOPED
were similar to those reported by Bender et al.,2 4whose
set of studies was in a similar population (obstetrical
patients). Again, the majority of RCTs gave inadequate
description of the randomization process (72%), blind-
ing (63%), and withdrawals (54%). Our study, which
evaluated RCTs from 1949 to 1999, confirms that fur-
ther work is needed to improve the quality of RCTs.
As mentioned previously, part of the difficulty in
evaluating methodological quality is due to poor
reporting. Often for blinding and withdrawal, we
could not differentiate between failure to perform
blinding and track withdrawals or failure to report
them. None of the RCTs were reported using stan-
dardized reporting criteria. Given the inadequacies of
reports examined in anesthesia so far, we advocate the
adoption of standardized criteria such as the CON-
SORT statement2 5 to improve quality of RCTs.
Our findings echo previous observations of the
validity and statistical concerns in anesthesia evidence.
There is room for improvement in the quality of non-
randomized and randomized studies of PDPH in
obstetrical patients. Median quality scores were low
for both types of studies. There were no differences in
quality between full papers and meeting abstracts.
This study is the first to evaluate the quality of
observational studies in anesthesia. Both reporting
and methodological quality (based on external validi-
ty, bias, confounding, and power) were poor with
median scores less than half of the maximum possible
score per category. No observational study in the
examined set evaluated power. This observation reit-
erates the concerns raised previously by other method-
In summary, we have compiled a bibliographic data-
base that covers the literature on obstetrical PDPH
from 1949 to 1999. We hope to update this database
on a regular basis. Examination of the architecture of
obstetrical PDPH research and the quality of observa-