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Repeated Measurements and Accounting for Change
Published in Mitchell G. Maltenfort, Camilo Restrepo, Antonia F. Chen, Statistical Reasoning for Surgeons, 2020
Mitchell G. Maltenfort, Camilo Restrepo, Antonia F. Chen
If we have data collected on a group of patients at the beginning of treatment and at the end of treatment, we can test whether they improved after treatment. If we have another group of patients who did not get the treatment but were measured at the same time in the same place, we can estimate the potential effect of treatment. However, once we begin looking at the same patient on multiple occasions, we have a new issue to consider. Statistical tests assume all observations are independent. A study with repeated observations violates this assumption so these tests become inappropriate. The technical name for this is pseudoreplication, and it can be addressed properly, if you use statistical tests that account for multiple measurements from the same source.
The human gut microbiota contributes to type-2 diabetes non-resolution 5-years after Roux-en-Y gastric bypass
Published in Gut Microbes, 2022
Jean Debédat, Tiphaine Le Roy, Lise Voland, Eugeni Belda, Rohia Alili, Solia Adriouch, Pierre Bel Lassen, Kazuyuki Kasahara, Evan Hutchison, Laurent Genser, Licia Torres, Camille Gamblin, Christine Rouault, Jean-Daniel Zucker, Nathalie Kapel, Christine Poitou, Geneviève Marcelin, Federico E. Rey, Judith Aron-Wisnewsky, Karine Clément
Our model of conventional juvenile microbiota-depleted mice was proposed as an alternative to germ-free rodents.26 This model has shown satisfactory engraftment capabilities after human-to-mice FMT.49–51 Here, 60% of the detected species within the recipient animals were found in their respective donors, a level concordant with the literature and to the level of axenic animals.52 We chose to use multiple donors, which allowed for a relative diversity in terms of patients’ phenotype and medications, which are known to impact the GM.30,53 Moreover, we followed the recommendations proposed by Walter and colleagues20 to limit statistical biases due to pseudoreplication (artificial inflation of the number of experimental units). Overall, we believe that these methodological precautions strengthen our observations.
Predictors of Need for First and Recurrent Emergency Medical Service Transport to Emergency Department after Dialysis Initiation
Published in Prehospital Emergency Care, 2020
A. J. Vinson, J. Bartolacci, J. Goldstein, J. Swain, D. Clark, K. K. Tennankore
In a secondary competing risk analysis, we examined time to recurrent EMS event after initiating dialysis using the Anderson-Gill counting approach, accounting for competing risks. Again, we used Fine and Gray’s proportional subhazards regression model to identify the association between patient characteristics and recurrent EMS-ED accounting for the competing risk of death or transplant. For those with no EMS-ED, survival time was from dialysis start to death, transplant or end of study. To account for individual level variation in EMS-ED use, the individual patient identifier was included in all models as a random effect. This is important given the non-independence of recurrent EMS-ED events for a given patient who may have a comorbidity or characteristic that makes them more prone to EMS-ED. If we did not use a random effect in our model, multiple EMS-ED events within a given patient would be considered as independent, which represents pseudoreplication and therefore, inflated Type I error rates (17). Time to each EMS-ED transport was determined from either dialysis start for the first EMS-ED presentation, or from the preceding date of EMS-ED use. Results were presented as sub-distribution hazard ratios with 95% confidence intervals and all models were adjusted for those covariates noted above.
Is Santa Claus an evening owl?
Published in Chronobiology International, 2019
One important limitation is the low sample size (N = 1) that should be increased in further studies; however, pseudoreplication has to be avoided. Unfortunately, I was not able to obtain any ethical clearing from the faculty for this study, and even more, I did not receive any signed informed consent, although I send many e-mails and letters to different (but probably wrong) addresses.