Comparison 6. Number of cannulation attempts.

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
6.1 Difficulty levels defined by original studies	11	958	Mean Difference (IV, Random, 95% CI)	‐0.29 [‐0.49, ‐0.09]
6.1.1 Difficult	9	568	Mean Difference (IV, Random, 95% CI)	‐0.33 [‐0.64, ‐0.02]
6.1.2 No restriction by intravenous access difficulty level	2	390	Mean Difference (IV, Random, 95% CI)	‐0.30 [‐0.50, ‐0.11]
6.2 Difficulty levels defined by the success rate with the landmark method	11	958	Mean Difference (IV, Random, 95% CI)	‐0.29 [‐0.49, ‐0.09]
6.2.1 Difficult	6	468	Mean Difference (IV, Random, 95% CI)	‐0.36 [‐0.75, 0.03]
6.2.2 Moderate	3	437	Mean Difference (IV, Random, 95% CI)	‐0.32 [‐0.47, ‐0.16]
6.2.3 Easy	1	35	Mean Difference (IV, Random, 95% CI)	0.10 [‐0.44, 0.64]
6.2.4 No data of the success rate	1	18	Mean Difference (IV, Random, 95% CI)	‐1.50 [‐3.50, 0.50]