The reason for this was that all these early studies lacked the microscope.

First, some studies may have lacked statistical power to detect interactions.

While the definitive studies are lacking, the former view received support from a 2004 meta-analysis of 13 small studies.

Like many dietary supplements, published studies demonstrating scientific evidence of its effectiveness and safety is lacking.

In addition to using a small number of patients, the study lacked a group that received a placebo for purposes of comparison.

Almost two decades later, such studies are still lacking.

However, long-term studies necessary to evaluate these effects are lacking.

But the study lacked a placebo group for comparison.

Prospective studies comparing one regimen with another are lacking.

Available studies lack sufficient power to extrapolate a standardized therapeutic regimen.