# MedStat Stutter

## Phantasies of a physicist fallen among physicians

### Box-Cox Transformations for linexp fits

January 15, 2020, 7:09 pm

The coefficients of linexp fits to gastric emptying curves are generally used in mixed-models to analyze group and meal difference. The distribution of the extracted parameters is often highly skewed, so before using linear models or estimates of reference ranges with functions in package referenceInterval or Hmisc, a transformation might be required.

From a large corpus of gastric emptying curves analyzed with nonlinear fits of the linexp function, the following recommendations for transformation were obtained using the boxcox and the logtrans function in package MASS:

### AUC (area under the curve) considered harmful

January 15, 2020, 6:58 pm

The title is stolen from Dijkstra.

Papers submitted to medical journals below the top rank are most often reviewed by medical reviewers who have used the Wilcoxon test as a catch-all in their active days. To smuggle a paper though their phalanx, garnish it generously with:

• p-values
• Wilcoxon-...

### The Ballot and the Bazaar

May 8, 2017, 11:55 am

Gastric emptying can be recorded by scintigraphy or by MRI techniques. Scintigraphy returns times series data of the meal volume, MRI gives the total content of the stomach, which includes meal and secretion. To quantify secretion and emptying in clinical studies, non-linear curves are fitted to the time series, which can give strange results. When the ballot fails, the bazaar comes to the rescue.