We conduct numerical experiments to examine two studies that reported preseismic anomalies in the ionospheric total electron content (TEC) and argued for the significance of their respective analyses based on statistical evaluations. The first study is Liu et al. (2018), who statistically studied the relationship between 62 M≥6 earthquakes in the Chinese interior over an 18-year period and the TEC, which was deduced from the Global Ionospheric Map. The TEC showed anomalies with specific polarities at set times during certain days that preceded the earthquakes. They defined alarms based on this and drew receiver operating characteristic curves, which yielded a significantly better performance (higher area under the curve (AUC) and lower p-value) than random alarms. We conduct this analysis using random synthetic earthquakes. The resulting AUC and p-values are very similar to those for real earthquakes, indicating that the high performance of the Liu et al. (2018) alarm is an artifact. The second study is Le et al. (2011), who classified the TEC time series into anomalous and non-anomalous days based on the TEC perturbation. They found that the anomalous day rate increased as the nucleation time of the earthquakes was approached, especially for larger and shallower earthquakes. We conduct the same analysis using random synthetic earthquakes. The anomalous day rate that is comparable to their result occurs in ~40 % of the 1,000 random trials, thereby suggesting that their result may also be an artifact.