Where's Waldo for appraisal practice

In a recent appraisal, I was analyzing market data when I discovered an outlier. The dataset contained homes that fit within a tight SqFt and age range. As you can see by the two box plots, one sale is significantly lower in reported sales price than all of the others within the past year. Looking at the SqFt box plot you can see this property is only slightly smaller than the other sales in the area. Once I placed these sales on a heat map, the reason became more apparent. The pale blue-green dot just above the subject indicator is this sale. This home backs up to a busy street. The sale price appears to be affected by the slightly smaller SqFt and external obsolescence. As defined by the Dictionary of Real Estate Appraisal 6th edition, external obsolescence is "A type of depreciation, a diminution of value caused by negative external influences and generally incurable on the part of the owner, landlord, or tenant." It appears this market doesn't think too kindly of properties adjacent to a busy street.