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Partial R-square was used to assess the level of overmatching.
Theoretically, the optimal algorithm has been demonstrated to outperform the greedy algorithm at the expense of computational costs .
However, in the context of our clinical study where the number of needed matched pairs was smaller than 50, it was not clear how large the difference would be in the performance of these algorithms.
Study participants are patients aged over 70 years who underwent scheduled major non-cardiac surgery.
The primary outcome was postoperative delirium from in-hospital interviews and medical record review.
Matching cases to controls according to baseline measurements of one or several confounding variables is done to control for the the effect from confounding variables.
A counter-matched study, in contrast, is when we matces cases to controls who have a different baseline risk factor exposure level.
The nested case-control study (NCC) design within a prospective cohort study is used when outcome data are available for all subjects, but the exposure of interest has not been collected, and is difficult or prohibitively expensive to obtain for all subjects.
A NCC analysis with good matching procedures yields estimates that are as efficient and unbiased as estimates from the full cohort study.
If the match procedure is carried out properly, and the selected controls are representative of the controls in the cohort study, then NCC loses little efficiency compared to the full cohort analysis .
NCC could offer better validity than the full cohort study because the match procedure allows for adjustment for both measured, and for unmeasured confounders .