Cohen's d calculator

library(shiny)
shinyUI(fluidPage(
  titlePanel("Calculation of Cohen's d for t-test"),
  sidebarLayout(
    sidebarPanel(
      helpText("Please input relevant information you collected from your data. The outcome will show you the absolute value of Cohen's d."),
      numericInput("numericM1", "What was the MEAN of the FIRST sample?", value = 0),
      numericInput("numericM2", "What was the MEAN of the SECOND sample?", value = 0),
      numericInput("numericSD1", "What was the STANDARD DEVIATION of the FIRST sample?", value = 0),
      numericInput("numericSD2", "What was the STANDARD DEVIATION of the SECOND sample?", value = 0),
      helpText("For more information on Cohen's d, please visit: rpsychologist.com/d3/cohend/")
    ),
    mainPanel(
      h2("Cohen's d"),
      helpText("Nowadays, it is usual to report the effect size along p-values. Cohen's d is one of such measures, and you can easily calculate it by providing the relevant statistics (Ms and SDs) obtained from your data. The error messages below will vanish once relevant data are provided."),
      plotOutput("plotAjnc"),
      textOutput("cohD"),
      textOutput("comment")
    )
  )
))

library(shiny)
shinyServer(function(input, output){
  output$plotAjnc <- renderPlot({
    SDpool <- sqrt(((input$numericSD1^2)+(input$numericSD2^2))/2)
    height <- (input$numericM1-input$numericM2)/SDpool
    plot(abs(height), ylab = "Cohen's d", ylim = c(0, 3), col = "steelblue", pch = 20, cex = 3, xlab = "", xaxt = "n")
    abline(h = 0)
    abline(h = 0.3, col = "red", lty = 2)
    abline(h = 0.6, col = "green", lty = 2)
    axis(1, xaxt = "n")
    })
  output$cohD <- renderText({
    cohenD <- (input$numericM1-input$numericM2)/sqrt(((input$numericSD1^2)+(input$numericSD2^2))/2)
    paste("The value of Cohen's d is", abs(round(cohenD, 3)), ".")
  })
  output$comment <- renderText({
    cohenD <- (input$numericM1-input$numericM2)/sqrt(((input$numericSD1^2)+(input$numericSD2^2))/2)
    if(cohenD<0.3) {print("Size of the effect is small.")}
    else if(c(cohenD>0.3 & cohenD<0.6)) {print("Size of the effect is medium.")} 
    else {print("Size of the effect is large.")}
})
})