Junoy Montolio
11 showed that the time of day, season, reliability indices (number of fixation losses, false negatives, and false positive), technical experience, and follow-up period have a clinically relevant influence on the MD test results. To determine the magnitude and importance of the GVE, we compared it with these factors. We excluded technical experience and follow-up period due to the lack of data on these factors. Hence, we focussed on the time of day, season, and the reliability indices. For time of day, the tests were stratified into four categories: performed before 10 AM, between 10 AM and 12 PM, between 12 PM and 2 PM, and after 2 PM. For season, the tests were also stratified into four categories, of 3 months each (March–May, June–August, September–November, December–February), based on the annual variation of retinal sensitivity.
11 The reliability indices were treated as continuous variables. Reliability indices include the percentage of fixation losses, the proportion of false positives, as well as the proportion of false negatives. We will refer to this model as the fixed-factor model. An example of the model fits for one location can be seen in
Figure 7. We compared the model fits using the RMSE, MAE, and 95
th percentile of the absolute errors. Furthermore, we determined the magnitude of the GVE compared with the factors by calculating their absolute means. A limitation of the two-stage approach occurs when there is sparse data, such as the season or time of day. Because each individual was analyzed separately, information could not be borrowed from the data set as a whole as done in the classical one-stage approach. Due to this limitation, we used the classical one-stage approach including 50 randomly selected individuals for this analysis.