Table 3.

Contextual factors and measurement methods.

Category and contextual factor			Data collection method
Physiological factors
	Age	Self-report [43,44]
	Sex	Self-report [36,43]
	Body weight	Fitbit [16] and self-report [43]
	BMI	Self-report [44]
	Body temperature	Diary [16]
	Heart rate	Fitbit [35,44] and MS Band [43]
	Menstrual cycle	Diary [16]
	Calorie in and out	Fitbit [16] and MS Band [43]
	Activity calorie	Fitbit [16]
Psychological factors
	Stress	Diary [16]
	Mood	Diary [16] and SleepApp [19]
	Tiredness	Diary [16]
	Dream	Diary [16]
	Sleep quality the previous night	SleepAsAndroid [20] and MS Band [43]
	Cognitive performance	Keystroke time [34] and click time [34]
Behavioral factors
	Steps	Fitbit [16,37] and MS Band [43]
	Distance walked	Fitbit [37]
	Active time	Fitbit [16,37]
	Exercise	SleepAsAndroid [20], MS Band [43], Polar [40], Garmin [42], and SleepApp [19]
	Coffee	Diary [16], SleepAsAndroid [20], and SleepApp [19]
	Alcohol	Diary [16], SleepAsAndroid [20], and SleepApp [19]
	Tobacco	Self-report [44] and SleepApp [19]
	Electronic device use	App use time (total and different app categories) [31], diary [16], Bing search logs [43], SleepApp [19], and campus network [36]
	Nap	Diary [16], SleepAsAndroid [20], and SleepApp [19]
	Location	Campus Wi-Fi [31] and Cortana [43]
	Social activity	GruMon (location estimation based on Wi-Fi signals) [31], diary [16], and Twitter [43]
	Mealtime	Diary [16], smartphone camera [42], SleepApp [19], and campus smart card [36]
	Waketime	SleepAsAndroid [20]
	Bedtime	Fitbit [37], IoTa sensor [42], and SleepApp [19]
Environmental factors
	Ambient temperature	Diary [16] and IoT sensor [42]
	Ambient humidity	Diary [16] and IoT sensor [42]
	Ambient light	Diary [16] and SleepAsAndroid [20]
	Ambient noise	SleepAsAndroid [20]
	Day of week	MS Band [43]

^aIoT: internet of things.