LikertMakeR

LikertMakeR logo

LikertMakeR synthesises Likert scale and related rating-scale data. Such scales are constrained by upper and lower bounds and discrete increments.

Purpose

The package is intended for

“reproducing” rating-scale data for further analysis and visualisation when only summary statistics have been reported,
Teaching. Helping researchers and students to better understand the relationships among scale properties, sample size, number of items, etc..
Checking the feasibility of scale moments with given scale and correlation properties

Functions in LikertMakeR are:

lfast() draws a random sample from a scaled Beta distribution to approximate predefined first and second moments
lexact() attempts to produce a vector with exact first and second moments
lcor() rearranges the values in the columns of a data set so that they are correlated to match a predefined correlation matrix

Rating scale properties

A Likert scale is the mean, or sum, of several ordinal rating scales. They are bipolar (usually “agree-disagree”) responses to propositions that are determined to be moderately-to-highly correlated and capturing various facets of a construct.

Rating scales are not continuous or unbounded.

For example, a 5-point Likert scale that is constructed with, say, five items (questions) will have a summed range of between 5 (all rated ‘1’) and 25 (all rated ‘5’) with all integers in between, and the mean range will be ‘1’ to ‘5’ with intervals of 1/5=0.20. A 7-point Likert scale constructed from eight items will have a summed range between 8 (all rated ‘1’) and 56 (all rated ‘7’) with all integers in between, and the mean range will be ‘1’ to ‘7’ with intervals of 1/8=0.125.

Alternative approaches

Typically, a researcher will synthesise rating-scale data by sampling with a predetermined probability distribution. For example, the following code will generate a vector of values with approximately the given probabilities.

```{r, eval = FALSE}

 n <- 128
 sample(1:5, n, replace = TRUE,
   prob = c(0.1, 0.2, 0.4, 0.2, 0.1)
 )

```

The functions lfast() and lexact() allow the user to specify exact univariate statistics as they might ordinarily be reported.

Install LikertMakeR

The development version of LikertMakeR is available from the author’s GitHub repository.

To download and install the package, run the following code from your R console:

```{r, eval=FALSE}

library(devtools) install_github(“WinzarH/LikertMakeR”)

```

Generating synthetic rating scales

To synthesise a rating scale, the user must input the following parameters:

n: sample size
mean: desired mean
sd: desired standard deviation
lowerbound: desired lower bound
upperbound: desired upper bound
items: number of items making the scale - default = 1
seed: optional seed for reproducibility
LikertMakeR offers two different functions for synthesising a rating scale: lfast() and lexact()

lfast()

lfast() draws a random sample from a scaled Beta distribution. It is very fast but does not guarantee that the mean and standard deviation are exact. Recommended for relatively large sample sizes.

Example: a five-item, seven-point Likert scale


x <- lfast(
  n = 256, 
  mean = 4.5, sd = 1.0, 
  lowerbound = 1, 
  upperbound = 7, 
  items = 5
  )

Example: an 11-point likelihood-of-purchase scale


x <- lfast(256, 2.5, 2.5, 0, 10)

lexact()

lexact() attempts to produce a vector with exact first and second moments. It uses the Differential Evolution algorithm in the ‘DEoptim’ package to find appropriate values within the desired constraints.

lexact() may take some time to complete the optimisation task, but is excellent for simulating data from already-published reports where only summary statistics are reported.

Example: a five-item, seven-point Likert scale


x <- lexact(
  n = 32, 
  mean = 4.5, 
  sd = 1.0, 
  lowerbound = 1, 
  upperbound = 7, 
  items = 5
  )

Example: an 11-point likelihood-of-purchase scale


x <- lexact(32, 2.5, 2.5, 0, 10)

Example: a seven-point negative-to-positive scale with 4 items


x <- lexact(
  n = 32, 
  mean = 1.25, 
  sd = 1.00, 
  lowerbound = -3, 
  upperbound = 3, 
  items = 4
  )

Correlating vectors of synthetic rating scales

LikertMakeR offers another function, lcor(), which rearranges the values in the columns of a data set so that they are correlated at a specified level. It does not change the values - it swaps their positions in a column so that univariate statistics do not change, but their correlations with other vectors do.

To create the desired correlations, the user must define the following objects:

data: a starter data set of rating-scales
target: the target correlation matrix

lcor() Examples

generate synthetic data


set.seed(42) # for reproducibility

n <- 64
x1 <- lfast(n, 3.5, 1.00, 1, 5, 5) 
x2 <- lfast(n, 1.5, 0.75, 1, 5, 5) 
x3 <- lfast(n, 3.0, 1.70, 1, 5, 5) 
x4 <- lfast(n, 2.5, 1.50, 1, 5, 5)   

mydat4 <- cbind(x1, x2, x3, x4) |> 
    data.frame()

head(mydat4)
cor(mydat4) |> round(3)

Define a target correlation matrix


tgt4 <- matrix(
c(
  1.00, 0.50, 0.50, 0.75,
  0.50, 1.00, 0.25, 0.65,
  0.50, 0.25, 1.00, 0.80,
  0.75, 0.65, 0.80, 1.00
),
nrow = 4
)

Rearrange values in each column to achieve desired correlations


new4 <- lcor(data = mydat4, target = tgt4)

cor(new4) |> round(3)

three starting vectors and different target correlation matrix


mydat3 <- cbind(x1, x2, x3) |> data.frame()

tgt3 <- matrix(
  c(
     1.00, -0.50, -0.85,
    -0.50,  1.00,  0.60,
    -0.85,  0.60,  1.00
  ),
  nrow = 3
)

new3 <- lcor(mydat3, tgt3) 

cor(new3) |> round(3)

To cite LikertMakeR

here’s how to cite this package:


Winzar, H. (2022). LikertMakeR: Synthesise and correlate rating-scale data with predefined first & second moments, <https://github.com/WinzarH/LikertMakeR>