To control for an additional extraneous factor, the tests described in the previous section may be extended to allow for a stratification of the data; as before, the score statistics U, and their variances, V, are calculated for each stratum and simply added over strata.
One type of confusion may arise from the distortion of the effect of an exposure of interest by some extraneous factor when the effect of the extraneous factor is mistaken for or mixed with the actual exposure effect.
However, we cannot distinguish whether the changes we report are explained by a disruption of a circadian influence or an extraneous procedural factor.
Confounding happens when the effect of at least one extraneous factor (e.g., body mass index, BMI) is mixed with the effect of an exposure of interest (25(OH D), thus distorting the estimate of the latter [ 89].
Our negative results are even more surprising because in the last 10 12 years of the time-series data the guanaco population fluctuated remarkably, suggesting some extraneous factor in addition to between population density, maybe climatic variables.
Such physiological generalisations likely oversimplify game demands, whereby a host of extraneous factors also contribute to the game's bandwidth of physiological responses.
Furthermore, while the study coordinator would encourage the participants to provide their best effort during the testing period, the effort exerted by the participant may have been influenced by a variety of extraneous factors such as fatigue and dehydration.
At the on-line level, unless mandated by extraneous factors, a surgical crew performs all surgical cases assigned to the OR, sequencing them in a non-increasing order of their largest expected surgical time.
These observations remind us that clinical trials occur in a real world context and enrollment can be seriously impacted by a wide range of extraneous factors, some that are beyond the control of the investigative team and others that can be addressed during protocol development.
The randomisation of wards to conditions made it possible to separate the effects of the intervention from extraneous factors in a way that a pre- and post-test within a single setting could not.
