Although the findings are important, there are some serious study limitations to be considered.
Confidence in estimates of effects was diminished by serious concerns about study limitations, which were primarily raised by unclear and incomplete reporting of study methods and procedures by authors of included studies.
However, we rated the quality of this evidence as very low, due to very serious concerns about study limitations and not having enough evidence (only one study with outcome data from 50 participants).
Studies were excluded if serious limitations to study quality and major uncertainty about directness existed.
Because of serious limitations of study quality and important inconsistency of the observational studies, the level of evidence for an association between subnormal vitamin B12 concentrations and anaemia in older individuals was considered low.
Two RCTs exhibited serious limitations in study quality and execution: Keeley in 2007 had a nearly 50% dropout rate [ 19], and Drakulovic and colleagues in 1999 stopped prematurely after interim analysis showed a very large treatment effect in favor of the 45° elevation [ 8].
This organization is critical to the urine-concentrating activity of the metanephros, so lack of a good culture model to allow the development of cortico-medullary differences to be studied is a serious limitation to the field.
For example, what is a "serious" limitation in study quality or an "important" inconsistency among effect sizes?
One study had serious methodological limitations due to high risk of attrition bias [37].
