Quantifying the Difference Between Self-Reported and Global Positioning Systems-Measured Journey Durations: A Systematic Review

Figures & data

Table 1.  Criteria used to assess quality of studies

Criteria	Possible score
	0	1	2
Year of study^a	Pre 2005	2005–present	–
Population size	<50	>50, but ≤100	>100
Number of measured trips	<100	>100, but ≤200	>200
Data quality^b	Low	Medium	High
Population representative?	No	Yes	–
Modes measured	1	2 or more	–
Peer review	No	Yes	–
^aYear of study meant as indicator of device quality. Based on assumption that devices and software have improved since 2005.
^bData quality is a subjective judgement regarding the proportion of collected data (trips) that were eligible and/or retained for analysis.

Figure 1. Study flow chart. Selection and screening process for included studies.

Figure 2. A representation of analysis types. Matched-trip analysis finds the same trip from both methods and compares the difference in duration. Trips that are in one measure but not the other are discarded. The average difference is presented; unmatched-trip analysis calculates the average duration from self-report and compares it to the average duration from GPS. Trips that are in one measure but not the other are included.

Table 2.  Quality criteria of 14 included studies ordered by date

Study	Criteria							Total score
	Year of study (0/1)	Population size (0/1/2)	Measurements (0/1/2)	Data treatment quality (0/1/2)	Representative sample (0/1)	Travel modes (0/1)	Peer review (0/1)
Murakami and Wagner (1999)	0	2	1	2	1	0	1	7
Bachu et al. (2001)	0	0	0	1	1	0	1	3
Stopher et al. (2002)	0	0	0	2	0	0	1	2
Wolf, Oliveira, et al. (2003)	0	2	2	2	1	0	1	8
Schönfelder and Samaga (2003)	0	0	2	2	0	0	1	5
Stopher et al. (2007)	1	2	1	2	1	1	1	9
Schuessler and Axhausen (2009)	1	2	2	1	1	1	1	9
Krygsman and Nel (2009)	1	1	2	2	1	1	1	9
Bricka et al. (2009)	1	1	1	0	1	1	1	7
Stopher and Greaves (2010)	1	2	1	2	1	1	1	9
Blanchard et al. (2010)	1	1	1	1	0	0	1	5
Cho et al. (2010)	1	0	0	2	0	0	1	4
Department for Transport (2009)	1	2	2	2	1	1	0	9
Department for Transport (2011)	1	2	2	2	1	1	0	9

Table 3.  Included studies (n = 8) by date that compare GPS and self-reported journey duration, absolute difference (minutes), and percentage difference (GPS comparator)

Study result	Analysis	Result—average journey duration (minutes)		Difference per trip
		GPS	Self-report	Absolute (minutes)	95% CI of difference	Percentage
Bachu et al. (2001)	Unmatched	10.1	12.3	+2.2	2.2	+21.8
Stopher et al. (2002)	Unmatched	17.9	31.4	+13.5	–	+75.4
	Matched	27.8	31.4	+3.6	–	+12.9
Wolf, Oliveira, et al. (2003)^a	Matched*	12.3	15.6	+3.3	1.3^b	+26.8
	Matched**	11.1	14.9	+3.8	1.5^b	+34.2
	Matched***	11.4	14.7	+3.3	1.4^b	+28.9
Stopher et al. (2007)	Matched	13.0	14.2	+1.2	^c	+9.2
Department for Transport (2009)	Unmatched	15.0	22.0	+7.0	–	+46.7
	Matched	15.0	18.0	+3.0	–	+20.0
Stopher and Greaves (2010)	Matched	17.1	18.9	+1.8	–	+10.5
Blanchard et al. (2010)	Matched	35.4	41.9	+6.5	–	+18.4
Cho et al. (2010)	Unmatched	12.5	20.3	+7.8	4.5^b	+62.4
^aWolf 2003 presented results separately for three locations: (*) San Diego (**) Alameda, and (***) Sacramento.
^bResults significant at 95% level based on our analysis.
^cReported to be significant at 95% level.

Table 4.  Characteristics of included (n = 8) studies

Study	Location	Study population as reported by authors	Age range	Collection period	GPS unit(s) as reported by authors	Self-report measure	Travel dimension assessed
Bachu et al. (2001)	Louisiana, USA	10 households	27–62 years	1 day	Garmin GPS III+	Time use diary	Driving
Stopher et al. (2002)	Sydney, Australia	5 households	n/a	1 day	In-vehicle GeoLogger	Time use diary	Driving
Wolf, Oliveira, et al. (2003)	San Diego, Sacramento and Almeda, USA	Data from 254 households (517 surveyed)	n/a	1 day	GeoLogger	Travel diary and CATI	Driving
Stopher et al. (2007)	Sydney, Australia	70 households recruited; data from 45 households	15+ years	1 day	In-vehicle and wearable devices	Sydney Household Travel Survey (face-to-face interview)	Walking and driving
Department for Transport (2009)	United Kingdom	90 eligible households; 52% agreed; 134 eligible adults; 121 agreed; and 106 completed protocol	16+ years	7 days	Amtel BTT08	UK National Travel Survey (recall diary)	All modes
Stopher and Greaves (2010)	Victoria, Australia	58 complete households and 18 partially complete. Take up rate 12–56%	14+ years	1 day	Amtel GPS device	VISTA07 Travel diary	All modes
Blanchard et al. (2010)	Ontario, Canada	n = 61 (57% women)	67–92 years (Mean = 80.4)	1 week	CarChip E/X^® (Davis Instruments) and an Otto Driving Mate (Otto; Persen Technologies Inc.)	24 h daily activity diary	Driving
Cho et al. (2010)	North Carolina, USA	n = 40 adult volunteers (21 women)	Adults	4 days	Garmin Foretrex 201	2 × 2 day trip diary	Walking

Table 5.  Studies that were excluded (n = 6) as the analysis was between incomparable datasets

Study	Result—average journey duration (minutes)		Difference per trip
	GPS	Self-report	Absolute (minutes)	95% CI of difference	Percentage
Murakami and Wagner (1999)^a	14.2	13.9	−0.3	–	−2.1
Schönfelder and Samaga (2003)^b	24.4	58.7	+34.3	–	+140.6
Schuessler and Axhausen (2009)^c	26.2	14.8	−11.4	–	−43.5
Krygsman and Nel (2009)^d	42.7	24.4	−18.3	–	−42.9
Bricka et al. (2009)^e	13.0	18.0	+5.0	0.1	+38.5
Department for Transport (2011)^f	51.0	21.0	−30.0	–	−58.8
^aCompares six days of GPS data to nine day of recall data.
^bCompares data from GPS to data from a separate National Travel Survey. Data shown for fulltime workers; also available for retirees.
^cCompares data from GPS to data from a separate National Travel Survey. Self-report duration averaged from 3 sites presented.
^dCompares self-report data that included weekend travel to GPS data for week days only.
^eCompares data from two matched groups.
^fCompares data from larger sample using diary (n = 1726) to sub-sample who also carried GPS (n = 897).

Table 6.  Aggregated absolute and percentage difference between GPS and self-reported journey duration, for all results, for unmatched-trip analysis results and for matched-trip analysis results

Analysis type	Average journey duration (min)		Difference per trip
	GPS	Self-report	Absolute (min)	Percentage
All (n = 12)	15.3	19.7	+4.4	+28.6
Unmatched-trips (n = 4)	14.8	21.6	+6.8	+46.2
Matched-trips (n = 8)	15.6	18.8	+3.2	+20.3

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