The presence of extreme outlying observations
with good reproducibility (Table 51 of the online Data Supplement) suggests that concomitant analyte interferentes may exist in the assay used by laboratory E2.
This aspect of the simulation study was included to represent the practice whereby a researcher would attempt to identify and then remove any outlying observations
Still, big outlying observations
exist; particularly noticeable are again those associated with the Great Depression and the Second World War.
were identified with box-plots, the distribution normality was verified by the Shapiro-Wilk test.
While there is a large cluster of countries close to the regression line, this is largely a consequence of the outlying observations
In particular, extreme points, influential and outlying observations
, which might represent erroneous data or otherwise reflect unusual market conditions such as non-arm's length transactions, can seriously undermine the performance of parametric estimator.