Create Composite Variable

Load Packages

Haven

if (!require(haven)){
  install.packages("haven", dependencies = TRUE)
  require(haven)
}

Loading required package: haven

Psych

if (!require(psych)){
  install.packages("psych", dependencies = TRUE)
  require(psych)
}

Loading required package: psych

Summarytools

if (!require(summarytools)){
  install.packages("summarytools", dependencies = TRUE)
  require(summarytools)
}

Loading required package: summarytools

Warning in fun(libname, pkgname): couldn't connect to display ":0"

system might not have X11 capabilities; in case of errors when using dfSummary(), set st_options(use.x11 = FALSE)

Import Data

dataset <- read_sav("https://osf.io/kd4ej/download")

Scoring Data

#create dataframe with only relevant variables to work with
Extraversion <- data.frame (dataset$FFM_1, dataset$FFM_6, dataset$FFM_11, dataset$FFM_16, dataset$FFM_21, dataset$FFM_26, dataset$FFM_31, dataset$FFM_36)

#create list of 'keys'. The  numbers just refer to the order of the question in the data.frame() you just made. The most important thing is to mark the questions that should be reversed scored with a '-'. 
Extraversion.keys <- make.keys(Extraversion, list(Extraversion=c(1,-2,3,4,-5,6,-7,8)))

#score the scale
Extraversion.scales <- scoreItems (Extraversion.keys, Extraversion)

#save the scores
Extraversion.scores <- Extraversion.scales$scores

#save the scores back in 'dataset'
dataset$Extraversion <- Extraversion.scores[,]

#print the cronbach alpha
Extraversion.scales$alpha

      Extraversion
alpha    0.8141661