Table 3 Performances of binary classifiers of smoking status

Ever/never smokers

Training data

Accuracy (95% CI)

0.721 (0.693–0.747)

0.771 (0.744–0.795)

0.752 (0.725–0.777)

0.792 (0.766–0.816)

NIR (P: Acc > NIR)

0.658 (6.3 × 10⁻⁶)

0.658 (7.3 × 10⁻¹⁶)

0.658 (2.1 × 10⁻¹¹)

0.658 (< 2.2 × 10⁻¹⁶)

Kappa

0.444

0.527

0.480

0.577

Sensitivity

0.661

0.743

0.745

0.744

Specificity

0.835

0.824

0.764

0.885

PPV

0.885

0.890

0.858

0.925

NPV

0.562

0.625

0.610

0.658

External validation data

Accuracy (95% CI)

0.815 (0.784–0.842)

0.837 (0.808–0.863)

0.822 (0.791–0.849)

0.822 (0.791–0.849)

NIR (P: Acc > NIR)

0.637 (< 2.2 × 10⁻¹⁶)

0.637 (< 2.2 × 10⁻¹⁶)

0.637 (< 2.2 × 10⁻¹⁶)

0.637 (< 2.2 × 10⁻¹⁶)

Kappa

0.624

0.661

0.627

0.633

Sensitivity

0.766

0.818

0.814

0.792

Specificity

0.900

0.869

0.835

0.873

PPV

0.931

0.917

0.896

0.917

NPV

0.686

0.731

0.719

0.705

Current/former smokers

Training data

Accuracy (95% CI)

0.707 (0.671–0.740)

0.512 (0.474–0.550)

0.700 (0.664–0.733)

0.757 (0.723–0.788)

NIR (P: Acc > NIR)

0.522 (< 2.2 × 10⁻¹⁶)

0.522 (0.715)

0.522 (< 2.2 × 10⁻¹⁶)

0.522 (< 2.2 × 10⁻¹⁶)

Kappa

0.416

0.025

0.403

0.516

Sensitivity

0.658

0.504

0.625

0.701

Specificity

0.761

0.521

0.781

0.817

PPV

0.750

0.535

0.758

0.808

NPV

0.670

0.490

0.656

0.715

External validation data

Accuracy (95% CI)

0.646 (0.600–0.689)

0.541 (0.494–0.587)

0.619 (0.573–0.664)

0.674 (0.629–0.717)

NIR (P: Acc > NIR)

0.576 (1.3 × 10⁻³)

0.576 (0.940)

0.576 (0.03)

0.576 (9.9 × 10⁻⁶)

Kappa

0.318

0.093

0.251

0.373

Sensitivity

0.825

0.603

0.706

0.861

Specificity

0.513

0.494

0.555

0.536

PPV

0.556

0.468

0.539

0.578

NPV

0.799

0.628

0.719

0.839