It's training data. There's 17 suicidal and 17 non-suicidal scans, for a total of 34 scans. They trained 34 models, leaving one scan out each time. Of those 34 models, 31 correctly predicted the left-out scan.
IANAStatistician, but this seems like a trash result.
IANAStatistician, but this seems like a trash result.