Growth Lab

An interactive Shiny application for exploring vitamin C dose and supplement differences.

A reproducible introduction to group comparisons.

Growth Lab helps beginning R users explore an experiment without writing analysis code.

• 60 guinea pigs, with one response per animal.
• Three doses: 0.5, 1 and 2 mg/day.
• Two supplements: orange juice (OJ) and ascorbic acid (VC).
• Response: odontoblast length, recorded as len.

Each supplement/dose group contains 10 animals. The app preserves the recorded response scale because R's documentation does not specify a physical unit.

Source: Official R ToothGrowth documentation

Users choose a dose and select one or both supplements. They can also show individual observations on the boxplot.

The application responds immediately:

• server.R filters the selected observations.
• Reactive calculations update counts, means, medians and standard deviations.
• The chart and tables display the updated results.
• A comparison table reports OJ mean minus VC mean at each dose.

The How to use tab contains instructions, definitions and a worked example. Users can download the selected records as CSV.

m <- with(tg, tapply(len, list(dose, supp), mean))
result <- data.frame(Dose = as.numeric(rownames(m)), m)
result$Difference <- result$OJ - result$VC
knitr::kable(result, "html", digits = 2, row.names = FALSE)

At 0.5 mg/day, the OJ mean exceeds the VC mean by 5.25 on the recorded scale.

The R code calculates this table when the presentation is built. These descriptive results from guinea pigs do not establish effects in humans.

Open the live Shiny application

1. Choose 0.5 mg/day and keep both supplements selected.
2. Confirm 20 animals, group means of 13.23 and 7.98, and a difference of 5.25.
3. Change the dose to 2 mg/day and compare the updated results.
4. Read How to use for interpretation and limitations.

View the ui.R and server.R source on GitHub