Prior studies evaluating predictors of pain-related outcomes following treatment for sciatica have been limited by methodological problems, including retrospective study design, use of unvalidated outcome measures, and short-term follow-up periods.
With a few exceptions, the delinquent literature suffers from methodological problems, including biased sampling methods, small numbers of subjects, failing to objectively diagnose conduct disorder, incorrect use of specific statistical procedures, and lacking of appropriate control groups.
Gaps in knowledge are attributed to specific conceptual and methodological problems, including the lack of basic knowledge about pain behavior, over-reliance on an invasive short-term pain model, pain measurement issues, and lack of knowledge about confounders.
In general, available studies still suffer from methodological problems including small sample size, limitations of retrospective chart review, lack of standardized measures, overemphasis on inpatients, and lack of longitudinal data.
Human imaging studies of DAT availability in relation to chronic tobacco smoking are sparse and have generated conflicting results [28, 33] possibly related to methodological problems including the choice of radioligand and sample size.
Generally, cluster randomized trials, are susceptible to a range of methodological problems including selection bias [ 18].
Other methodological problems include use of multiple outcome measures not adjusted for multiple comparisons (e.g., Colom et al. 2010), as well as use of cut-off points selected retrospectively with risk of false-positive findings (e.g., Swann et al. 1999).
Other methodological problems include incomplete or inadequate blinding of outcome assessment and incomplete reporting on losses to follow-up (Table 2).
Common methodological problems include violation of the assumptions necessary for the statistical tests used, selection of an inappropriate sample of subjects, lack of true variance in the levels or categories within the sample tested, low prevalence of results across the full spectrum of test scores, and skewed or assymetrical distribution of data.
Their findings are similar to that of Donegan and colleagues, suggesting that the main methodological problems included unclear understanding of assumptions, incomplete inclusion of relevant studies, flawed or inappropriate methods, lack of similarity assessment and inappropriate combination of direct and indirect evidence.
It seems, therefore, that the detection of genetic variation for DA in this genus appears to be basically a methodological problem, including statistical power and the environmental conditions where the experiments are performed.
