Method for identifying a set of Reliable Negative examples from unlabeled data

Hello,

I am looking for confirmation on how I handled identifying a set of reliable negative examples from unlabeled data.  I have seen numerous methods performed; however, nothing specific about the approach I took (which isn’t to say it isn’t out there, I just haven’t seen it throughout my research).  Some background: the dataset that I’m working with has a set of positive examples (n = 964) and a larger set of unlabeled data (n = 8,107).  I do not have a set of negative examples.  I have attempted to run a one-class SVM but am not having any luck. So, I decided to try to identify a set of reliable negatives from the unlabeled data to be able to run a traditional regression model.  The approach I took was to run a local outlier factor (LOF) on all of my data to see if I could isolate a set of examples that have an outlier score that is completely different than my positive examples.  The chart below shows the distribution of scores between my positive class (lead = 1) and my unlabeled data (lead = 0).  As can be seen, the positive examples (minus the 1 example with an outlier score near 5,750) are all clustered at or below an outlier score of 2,000.

From here, I selected all of the examples from this output where lead = 0 (to ensure I’m only grabbing unlabeled data) and outlier score ≥ 2001 (the highest lead outlier score is 2,000.8) to use as my set of reliable negative examples (n = 315).  I then created a dataset of all of my positive examples plus the set of reliable negatives (n = 1,279) and fed this into a logistic regression model.  I am getting really great performance out of both the training and testing sets, which is making me question my methods.  Here is the training performance table:

•  Training AUC: 0.968 +/- 0.019 (mikro: 0.968)

Here is the testing performance table:

•  Testing AUC: 0.973

My questions are:

• Does the logic behind how I identified a set of reliable negatives makes sense? Are there any obvious (or not so obvious) flaws to my thinking?
• By constructing my final dataset in this way, am I making it too easy for the model to correctly classify examples?

Thank you for any help and guidance.

Kelly M.