Med. Weter. 82 (7), 335-341, 2026
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| BETÜL DAĞOĞLU HARK, SEMA ALAŞAHAN, CAFER TAYYAR ATEŞ, MAHMUT ŞAMİL ŞAMLI |
| Calibrated two-threshold rejection option classification of shape-index extremes in quail eggs using weight and shell color |
| The shape index (SI) is an indicator that quantifies egg shape and is associated with quality/hatching outcomes. However, direct measurement of SI in the field requires time and labor. The aim of this study is to develop and validate a probability-calibrated, two-threshold rejection option policy that can distinguish SI outliers (LOW/HIGH) in quail eggs using only weight and shell color, without measurement. In a dataset of 1,031 eggs (color: brown 61.9%, grayish white 38.1%), SI extremes were defined empirically (Q0.25 ≈ 67.20, Q0.72 ≈ 76.20). A classifier based on Hist Gradient Boosting was built using weight + color inputs. The probabilities obtained in the out-of-fold (OOF) scheme were corrected by sigmoid calibration. Two probability thresholds plo, phi were selected on the OOF distribution through a coverage-targeted search, and the final model was refined in two phases by “snapping” to the model’s discrete probability support points. The final policy produced approximately 61.4% coverage within the extreme tails with plo ≈ 0.527 and phi ≈ 0.761, while the accepted subset provided balanced accuracy (BA) ≈ 0.72 (95% CI [0.67 – 0.77]). The proportion of outliers in the entire data was 53.1%, and the expected overall automation (acceptance × outlier rate) was calculated to be ≈ 32.6%. The reject region made the risk-coverage balance controllable by directing uncertain samples to measurement. Calibrated probabilities, OOF threshold setting, and a two-threshold rejection policy can reliably identify SI outliers based solely on two observable phenotypes. This approach provides a scalable pre-screening layer that reduces measurement burden in incubation and quality control lines. It can be further enhanced in the future with microstructure and line/age-stratified designs. |
| Keywords: shape index; quail; shell color; rejection option; probability calibration; out-of-fold; two-threshold policy |