Table 2.

Confounding factors.

Confounding factor	Common gaming behavior
Hero type a
Strength	Strength-type heroes are mainly responsible for dealing with the physical damage from the opposing team and controlling the opposing heroes. Moving slowly and heavily without much flexibility, most strength-type heroes are responsible for melee. In the game, strength-type heroes frequently use skills to increase the attack speed, movement speed, health points (HP), physical defense points, magical defense points of their own or their teammates, decrease the HP of opposing heroes, impair their attack speed, movement speed, physical defense points, and magical defense points, and even disable them. When combating together with teammates, strength-type heroes usually stand in the front of the team and deal with heavy physical damage from the opposing team.
Agility	Agility-type heroes tend to deliver the highest physical damage. Moving rapidly with great flexibility, agility-type heroes usually make attacks at middle and remote range. As the team core in the game, agility-type heroes often kill more opposing heroes than their teammates. Agility-type heroes frequently participate in the team fights on the middle and later stage.
Intelligence	Intelligence-type heroes often act as supporting roles for their teammates to deliver physical damage when facing with opposing heroes and typically combat at remote range. In a game, intelligence-type heroes frequently cast spells. They can increase the attack speed, movement speed, HP, physical defense points, magical defense points of their own or their teammates, decrease opposing heroes’ HP.
Lane a
Dead	Against the safe lane of the opposing team, the dead lane is where your own creeps get closer to the opposing unit’s defensive towers, thereby making it easier for opposing heroes to kill your hero and making it harder for your hero to kill more lane creeps, neutral creeps and heroes of the opposing team. As a result, fewer experience and gold are gained, and your hero level could be relatively low.
Mid	Being the shortest lane, the mid lane is where you can meet more opposing creeps. Additionally, the distance between the mid lane and the neutral creeps is close, so your hero can kill more creeps and neutral creeps here, gaining more gold and higher level. Mid-lane heroes not only kill opposing heroes along this lane but also support teammates in other lanes to kill opposing heroes.
Safe	Being the longest lane, the safe lane is where the opposing creeps get closer to your defensive towers, making it easier for your heroes to kill more creeps, neutral creeps and opposing heroes. Safe lane heroes can scale well without turning to other lanes.
Historical game duration b	The longer a player’s historical game duration is, the more skilled the player is at operating various heroes. With more time spent on the game, a player knows better about the responsibilities of his or her hero and acquires more gaming experience.
Rankc
None	The higher a player’s rank is, the better the player knows about the abilities of each hero. Higher rankers can more flexibly and skillfully control their heroes.
Herald
Guardian
Crusader
Archon
Legend
Ancient
Divine
Immortal

^aVideo recording.

^bGame history data.

^cOnline questionnaire.