MedStat Stutter

Phantasies of a physicist fallen among physicians

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.

Multiple indexing with Stan

May 8, 2017, 11:54 am

Summary

Using vectors for indexed access to ragged arrays in Stan

volume ~ normal(
v0[record] .* (1+ kappa[record] .* (minute ./ tempt[record])) .*
exp(-minute ./ tempt[record]), sigma);

Fitting gastric emptying time series

Gastric volume times serie measured by MRI techniques can have an initial volume overshoot due to secretion. To estimate half-times and the degree of overshoot, the author of this blog has introduced the linexp function [@Fruehauf2011] with three parameters to complement the power exponential function used in earlier research [@Elashoff1982, @Elashoff1983b] with scintigraphic data.

linexp:

v = v0* (1+t*kappa/tempt)*exp(-t/t_{empt})

Crossover design with unequal weights

March 30, 2017, 6:21 pm

For a clinical study we needed a randomization table with the option to use unequal cell counts, e.g n = 8 for treatment 1 and 2 and n=12 for treatment 3 and 4. Using the R package by Kornelius Rohmeyer, I have written a little web app with Shiny.

Importing SQLite data into Excel 2013

March 30, 2017, 6:20 pm

You can find many post how to access an SQLite database from Excel, for example on Stack overflow. Often, the method uses VBA, or some older version of Excel, and I could not get things to work with my settings:

• Windows 10, 64 bit
• Virus Norton 360 premier
• Office 2013, 32 bit. Even Microsoft...