Multiple comparisons tests (MCTs) are performed several times on the mean of experimental conditions. When the null hypothesis is rejected in a validation, MCTs are performed when certain experimental conditions have a statistically significant mean difference or there is a specific aspect between the group means. A problem occurs if the error rate increases while multiple hypothesis tests are performed simultaneously. Consequently, in an MCT, it is necessary to control the error rate to an appropriate level. In this paper, we discuss how to test multiple hypotheses simultaneously while limiting type I error rate, which is caused by α inflation. To choose the appropriate test, we must maintain the balance between statistical power and type I error rate. If the test is too conservative, a type I error is not likely to occur. However, concurrently, the test may have insufficient power resulted in increased probability of type II error occurrence. Most researchers may hope to find the best way of adjusting the type I error rate to discriminate the real differences between observed data without wasting too much statistical power. It is expected that this paper will help researchers understand the differences between MCTs and apply them appropriately.

The previous articles of the Statistical Round in the Korean Journal of Anesthesiology posed a strong enquiry on the issue of null hypothesis significance testing (NHST). P values lie at the core of NHST and are used to classify all treatments into two groups: "has a significant effect" or "does not have a significant effect." NHST is frequently criticized for its misinterpretation of relationships and limitations in assessing practical importance. It has now provoked criticism for its limited use in merely separating treatments that "have a significant effect" from others that do not. Effect sizes and CIs expand the approach to statistical thinking. These attractive estimates facilitate authors and readers to discriminate between a multitude of treatment effects. Through this article, I have illustrated the concept and estimating principles of effect sizes and CIs.

Porcine epidemic diarrhea virus (PEDV) has plagued the domestic swine industry in Korea causing significant economic impacts on pig production nationwide. In the present study, we determined the complete nucleotide sequences of the spike (S) glycoprotein genes of seven Korean PEDV isolates. The entire S genes of all isolates were found to be nine nucleotides longer in length than other PEDV reference strains. This size difference was due to the combined presence of notable 15 bp insertion and 6 bp deletion within the N-terminal region of the S1 domain of the Korean isolates. In addition, the largest number of amino acid variations was accumulated in the S1 N-terminal region, leading to the presence of hypervariability in the isolates. Sequence comparisons at the peptide level of the S proteins revealed that all seven Korean isolates shared diverse similarities ranging from a 93.6% to 99.6% identity with each other but exhibited a 92.2% to 93.7% identity with other reference strains. Collectively, the sequence analysis data indicate the diversity of the PEDV isolates currently prevalent in Korea that represents a heterogeneous group. Phylogenetic analyses showed two separate clusters, in which all Korean field isolates were grouped together in the second cluster (group 2). The results indicate that prevailing isolates in Korea are phylogenetically more closely related to each other rather than other reference strains. Interestingly, the tree topology based on the nucleotide sequences representing the S1 domain or the S1 N-terminal region most nearly resembled the full S gene-based phylogenetic tree. Therefore, our data implicates a potential usefulness of the partial S protein gene including the N-terminal region in unveiling genetic relatedness of PEDV isolates.

[1] The authors welcome the comment from J. E. Mazur and T. P. O'Brien [Mazur and O'Brien, 2012] on our recently published study [Choi et al., 2011]. In our paper, we investigated the geostationary Earth orbit (GEO) satellite anomalies archived by Satellite News Digest (SND) during 1997-2009 in order to search for possible influences of space weather on the anomaly occurrences. There were good relationships between geomagnetic activity (as measured by the Kp index) and anomaly occurrences of the GEO satellites; the satellite anomalies occurred mainly in the midnight-to-morning sector, and the anomalies were found more frequently in spring and fall than in summer and winter. A comparison of the SND data with data from Los Alamos National Laboratory satellites showed that low-energy (<100 keV) electrons exhibit behavior similar to that of spacecraft anomalies and implied that the spacecraft charging may be a primary contributor to the GEO spacecraft anomalies reported on the SND Web site (http://www.sat-index.co.uk). [2] Mazur and O'Brien [2012] point out that some anomalies used in our analysis were not obviously caused by space weather effects. In fact, we intentionally used all of the GEO satellite anomalies listed on the SND Web site in order to exclude a subjective selection effect. Our event list, chosen from the SND database, represented major satellite anomalies that had significant financial impacts. There were numerous minor satellite anomalies reported from many agencies, and we want to emphasize that their tendency was similar to that of our event list. While the number of events may not be large enough to analyze local time dependence, when the anomalies reported by SND from 2010 to 2011 (indicated in Figure 1 by star symbols) are included, it is very clear that the anomaly occurrences are more frequent at nighttime than during the daytime. [3] Mazur and O'Brien [2012] also mention the relationship between GEO satellite anomalies and charging effects. Internal charging may be concerned with high-energy electrons and independent of its local time, while external charging is related to low-energy electrons and dependent on its local time. As we noted in Choi et al. [2011], the flux of 100 keV electrons on GEO orbit shows nonuniform distribution on the local time, yet these electrons don't have enough energy to penetrate satellite walls and charge internal components. At this moment, we don't fully understand the mechanism by which charged particles bring about the anomalies. [4] We support the proposal made by Mazur and O'Brien [2012] that an agency be established to maintain adequate and open anomaly and abnormality lists containing all information about events. We also anticipate that our paper will serve as encouragement to all the agencies concerned to make their anomaly data publicly available and to investigate an occurrence mechanism of spacecraft anomaly. References

2 Charged particles exhibit the Hall effect in the presence of magnetic fields. Analogously, ferromagnetic skyrmions with non-zero topological charges and finite fictitious magnetic fields exhibit the skyrmion Hall effect, which is detrimental for applications. The skyrmion Hall effect has been theoretically predicted to vanish for antiferromagnetic skyrmions because the fictitious magnetic field, proportional to net spin density, is zero. We experimentally confirm this prediction by observing currentdriven transverse elongation of pinned ferrimagnetic bubbles. Remarkably, the skyrmion Hall effect, estimated with the angle between the current and bubble elongation directions, vanishes at the angular momentum compensation temperature where the net spin density vanishes. This study establishes a direct connection between the fictitious magnetic field and spin density, offering a pathway towards the realization of skyrmionic devices.