Literature regarding content analysis often presents the estimation of reliability as a part of the development phase of a coding scheme, for example to inform a revision (Krippendorff, 2019; Kuckartz, 2018; Mayring, 2015; Schreier, 2012). If the reliability is considered to be sufficient, the main study starts. Often, the reliability of the codings of this main study is not further controlled, as it is assumed that the reliability estimates of the development phase hold for the entire main study. Sometimes however, researchers communicate and discuss their findings and assign a category to a coding unit by agreeing on the relevant category when the coding scheme is unclear.
With Iota Concept, the reliability of a coding scheme can be taken into account more explicitly during the main study. It provides the opportunity for error corrections, which is not possible with traditional measures such as Percentage Agreement, Cohen’s Kappa or Krippendorff’s Alpha.
The error correction of the Iota Concept is based on two ideas. First, an Assignment Error Matrix produces patterns of ratings for every coding unit. These patterns give hints which true category may be the source for this kind of observation. This requires at least two raters. Second, involving additional raters provides more information on a coding unit, which can improve the assignments. This idea is similar to the application of multiple items in questionnaires or tests where each item can be considered as a test for the phenomena of interest. Additional test are used to reduce errors.
In this vignette, we would like to continue our example of the exams from the first vignette and now want to show you how the error correction can be applied.
Applying the error correction of the Iota Concept requires
that all coding units of the core study are rated by at least two
raters. The error correction can be requested with the function
est_expected_categories(). This function calculates the
probability that a coding unit belongs to a specific true category under
the condition of the observed pattern. To illustrate the error
correction, a look into the data set is helpful.
library(iotarelr) head(iotarelr_written_exams) #> Coder A Coder B Coder C Sex #> 1 average average good female #> 2 average poor average male #> 3 poor average poor female #> 4 average average average female #> 5 poor average good female #> 6 poor poor average female
The first 6 rows of the data set show that the three raters do not agree on all coding units. While the raters agree on the first two exams, they disagree partially on exams 3 to 6. In particular, two raters consider exam 3 to be average while one rater considers this exams to be good. Thus, there seems to be some kind of error and it is not clear which category should be assigned to exam 3.
To solve this problem, we must first estimate the Assignment
Error Matrix. In the next step, we pass the estimated
Assignment Error Matrix to the function
est_expected_categories() and use the ratings as our data
source. The results are saved in the object
<-compute_iota2( res_iota2data=iotarelr_written_exams[c("Coder A","Coder B","Coder C")], random_starts = 10, trace = FALSE) <-est_expected_categories( expected_categoriesdata=iotarelr_written_exams[c("Coder A","Coder B","Coder C")], aem=res_iota2$categorical_level$raw_estimates$assignment_error_matrix) head(expected_categories) #> Coder A Coder B Coder C prob_average prob_good prob_poor expected_category #> 1 average average good 4.843042e-01 0.36354882 0.15214698 average #> 2 average poor average 8.666331e-08 0.27607873 0.72392118 poor #> 3 poor average poor 5.704391e-16 0.12917318 0.87082682 poor #> 4 average average average 9.169907e-01 0.04109578 0.04191355 average #> 5 poor average good 9.027516e-09 0.48170163 0.51829836 poor #> 6 poor poor average 5.704391e-16 0.12917318 0.87082682 poor
The resulting object contains the ratings and additional columns. The columns contain the probability that a coding unit belongs to a specific true category. The most plausible category is always presented in the last column.
For the first row, the probability that this exam is truly an average one is about 48.4%. The chance that this exam represents truly a good exam is about 36.3% and that is is truly a poor exam is about 15.2%. Thus, it is most plausible to assign exam number 1 to the category “average”.
For exam number two, the probability that this exam is truly an average one is about 0.00%. The chance that this exam represents truly a good exam is about 27.6% and that is is truly a poor exam is about 72.4%. Thus, it is most plausible to assign exam number 2 to the category “poor”.
If the ratings were done by only one rater, these kind of errors would not become visible. For example, if the exams were rated only by rater A, exam 2 would have been assigned as an average exam, although it is more plausible to assign it to the category “poor”.
Estimating the category that is most likely true has several advantages: