However, because these studies require significant time and resources and often have limited external validity, they are less useful for monitoring overdiagnosis over time.
The exceptions were the studies that performed an unjustified statistical adjustment for lead time, 43 45 50 52 which we rated as having poor directness because these studies require additional assumptions about cancer progression, and one study which excluded data from the prevalence screening round.
Given the usual lack of direct benefit, ethicists say, these studies require particularly close monitoring, because they can pose a risk to a volunteer's health or life.
Because these structural connectivity studies require intensive labor, they are typically performed on a select set of neurons, and currently cannot provide information about how hundreds of neurons are connected.
Because such studies require a fair amount of time in a research unit, the subjects are usually people who need money and have a lot of time to spare: the unemployed, college students, contract workers, ex-cons, or young people living on the margins who have decided that testing drugs is better than punching a clock with the wage slaves.
Few field studies on hydrology of volcanic islands in the Atlantic Ocean have been developed focusing on soil and water temporal dynamics and conservation, mainly because such studies require data with high temporal resolution, and also due to the financial costs involved with field data acquisition at such remote places.
Furthermore, because scoping studies require a balance between feasibility, significance, and the breadth and comprehensiveness of information that is scoped [ 20], they are challenging to conduct.
Responsiveness of genes to perturbations is a dynamic property that was never studied systematically because such studies require the analysis of expression profiles of cells responding to a large variety of disturbances, and such databases did not exist before.
To the best of our knowledge, there are only a few studies to date that have studied this predictive potential, mainly because such studies require long patient follow-up.
At times, family members took part in several studies at once -- a violation of the rules because studies require that participants not be taking other medications, so that the data obtained relate only to the drug under study.
Of these participants, one reported to having agreed to use Depo-Provera because the study required contraceptive use although she had no intention of using it.
