Table 4 Subgroup analysis for the predicting value of ROX

Overall studies

9

0.67 (0.57–0.76)

0.72 (0.65–0.78)

2.4 (2.0–2.80)

0.46 (0.37–0.58)

5 (4–7)

0.75 (0.71–0.79)

Population

 COVID-19

4

0.71 (0.56–0.82)

0.73 (0.63–0.81)

2.60 (2.10–3.30)

0.40 (0.28–0.56)

7 (5–9)

0.78 (0.74–0.82)

 Other population

5

0.63 (0.48–0.75)

0.71 (0.60–0.80)

2.10 (1.70–2.70)

0.53 (0.40–0.70)

4 (3–6)

0.72 (0.68–0.76)

Acquisition time

 6 h after receiving HFNC

6

0.67 (0.54–0.78)

0.70 (0.60–0.78)

2.20 (1.80–2.80)

0.47 (0.35–0.63)

5 (3–7)

0.74 (0.70–0.78)

 Other time

3

0.73 (0.67–0.79)

0.74 (0.70–0.78)

2.84 (2.39–3.39)

0.36 (0.29–0.45)

7 (5–10)

0.79 (0.75–0.83)

Cut-off value

 Cut-off ≤ 5

5

0.67 (0.65–0.76)

0.71 (0.61–0.80)

2.3 (1.8–2.9)

0.48 (0.37–0.63)

5 (3–7)

0.74 (0.70–0.78)

 Cut-off > 5

4

0.59 (0.54–0.65)

0.83 (0.79–0.86)

3.5 (2.78–4.43)

0.49 (0.43–0.56)

7 (5–9)

0.78 (0.74–0.82)