Are Word Suggestions Beneficial? The Effect of Typing Efficiency and Suggestion Accuracy

Word suggestion is a common feature of typing interfaces, but previous studies have found unclear or negative impacts. We report on three studies controlling for word suggestion accuracy and typing efficiency. Our accuracy factor uses a new methodology based on common word suggestion metrics. Typing efficiency is controlled by device type in the first study, and by artificial impairments in the following two. Results show that suggestions are used less as typing efficiency increases, and only improve speed when highly accurate, even with low typing efficiency. Inline suggestions save about 4% more keystrokes and increase typing speed by 2 words per minute compared to a bar suggestions, though they are more distracting. Based on our findings, we propose a model linking suggestion usage to accuracy and typing speed, and discuss implications for designing automation features in typing systems.