Reliability Testing using Chronbach’s Alpha

Summary Table

reliability <- psych::alpha(reina, check.keys=FALSE)
## Some items ( Q3 Q6 Q17 Q20 Q28 Q33 Q36 Q40 Q52 Q57 Q67 Q68 ) were negatively correlated with the total scale and 
## probably should be reversed.  
## To do this, run the function again with the 'check.keys=TRUE' option
summary(reliability)
## 
## Reliability analysis   
##  raw_alpha std.alpha G6(smc) average_r S/N  ase mean   sd median_r
##       0.88      0.89    0.88      0.11 8.1 0.04 0.58 0.14     0.13

Chronbach’s Alpha if Items are Removed

Refer to std.alpha column

DT::datatable(round(reliability$alpha.drop,2), 
          extensions = c('FixedColumns',"FixedHeader"),
          options = list(scrollX = TRUE, 
                         paging=TRUE,
                         fixedHeader=TRUE))

Interpretation

Chronbach’s Alpha was used to measure the internal consistency of the 70-item multiple choice test that measures the vocabulary competence of the respondents. The result shows that the alpha value is acceptable, \(\alpha\) = 0.89 (refer to the std.alpha score in summary table). Moreover, removing items do not affect the internal consistency (refer to the std.alpha on the Chronbach’s Alpha if Items are Removed) that much since the \(\alpha\) values are almost equal with an exemption on item 52 which increases to \(\alpha\) value to 0.90 if removed. As such, removing some items specifically item 52 may be considered.

Item Analysis

DT::datatable(itemanalysis, 
          extensions = c('FixedColumns',"FixedHeader"),
          options = list(scrollX = TRUE, 
                         paging=TRUE,
                         fixedHeader=TRUE))

Interpretation

Item analysis was performed to measure the difficulty index (Diff.Index) and the Discrimination Index (Disc.Index) of each item in the test. The result shows that only items 18, 19, 45, 56, 58, 61, and 70 with an average difficulty index are considered to have an acceptable discrimination index compared to others. This means that most of the items need to be improved or rejected.

Session Information for Reproducibility

sessionInfo()
## R version 4.0.2 (2020-06-22)
## Platform: x86_64-w64-mingw32/x64 (64-bit)
## Running under: Windows 10 x64 (build 18363)
## 
## Matrix products: default
## 
## locale:
## [1] LC_COLLATE=English_Philippines.1252  LC_CTYPE=English_Philippines.1252   
## [3] LC_MONETARY=English_Philippines.1252 LC_NUMERIC=C                        
## [5] LC_TIME=English_Philippines.1252    
## 
## attached base packages:
## [1] stats     graphics  grDevices utils     datasets  methods   base     
## 
## other attached packages:
## [1] DT_0.15          knitr_1.29       kableExtra_1.2.1 psych_2.0.8     
## 
## loaded via a namespace (and not attached):
##  [1] rstudioapi_0.11   xml2_1.3.2        magrittr_1.5      rvest_0.3.6      
##  [5] mnormt_2.0.2      munsell_0.5.0     viridisLite_0.3.0 colorspace_1.4-1 
##  [9] lattice_0.20-41   R6_2.4.1          rlang_0.4.7       stringr_1.4.0    
## [13] httr_1.4.2        tools_4.0.2       webshot_0.5.2     parallel_4.0.2   
## [17] grid_4.0.2        tmvnsim_1.0-2     nlme_3.1-148      xfun_0.17        
## [21] crosstalk_1.1.0.1 htmltools_0.5.0   yaml_2.2.1        digest_0.6.25    
## [25] lifecycle_0.2.0   htmlwidgets_1.5.1 glue_1.4.2        evaluate_0.14    
## [29] rmarkdown_2.3     stringi_1.5.3     compiler_4.0.2    scales_1.1.1     
## [33] jsonlite_1.7.1