Quantitative analysis of open-source data on metal detecting for cultural property: Estimation of the scale and intensity of metal detecting and the quantity of metal-detected cultural goods

Figures & data

Table 1. Proportions of metal-detected finds amongst reported finds in England and Wales, 2003–2008 (derived from Portable Antiquities Scheme, 2004, p. 80 – Table 6, p. 87 – Table 13; 2005, p. 7, p. 101 – Table 8; 2006, p. 113 – Table 3a, p. 122 – Table 8; 2009, p. 267 – Table 2a, p. 277 – Table 7; 2010, p. 26 – Table 4a, p. 32 – Table 8)

Year	# of finds with identified methods of discovery	# of finds by metal detecting	# of finds while metal detecting	Total # of MD-reported finds with identified methods of discovery	MD-reported finds as percentage of those identified
2003–2004	27,753	17,978	2,576	20,554	74.06
2004–2005	39,736	27,656	3,609	31,265	78.68
2005–2006	57,341	35,288	3,714	39,002	68.02
2006–2007	76,977	61,981	3,023	65,004	84.45
2007–2008	52,995	44,268	1,833	46,101	86.99
Mean avg	50,960.4	37,434.2	2,951	40,385.2	74.06
S. Deviation	18,616.43	16,792.92	776.35	16,711.70	7.70

Table 2. Rate of recovery of reportable finds by metal detectorists in England and Wales (derived from Portable Antiquities Scheme, 2004, p. 80 – Table 6, p. 87 – Table 13; 2005, p. 7, p. 101 – Table 8; 2006, p. 113 – Table 3a, p. 122 – Table 8; 2009, p. 267 – Table 2a, p. 277 – Table 7; 2010, p. 26 – Table 4a, p. 32 – Table 8)

Year	# of MD-reported finds	# of MD reporters	MDs as percentage of reporters	Finds per MD per year
2003–2004	20,554	1,726	72.64	11.91
2004–2005	31,265	1,751	76.93	17.86
2005–2006	39,002	3,439	58.74	11.34
2006–2007	65,004	4,328	63.00	15.02
2007–2008	46,101	4,232	65.47	10.89
Mean avg	40,385	3,095	67.36	13.05
S.D.	16,711.70	1,285.68	7.35	2.97
M. of error				2.60

Table 3. Means of recovery of reportable finds by metal detectorists in England and Wales (derived from Portable Antiquities Scheme, 2004, p. 80 – Table 6, p. 87 – Table 13; 2005, p. 7, p. 101 – Table 8; 2006, p. 113 – Table 3a, p. 122 – Table 8; 2009, p. 267 – Table 2a, p. 277 – Table 7; 2010, p. 26 – Table 4a, p. 32 – Table 8)

Year	# of reporting MDs	# of finds by metal detecting	“Deliberate” finds per MD per year	# of finds while metal detecting	“Incidental” finds per MD per year
2003–2004	1,726	17,978	10.42	2,576	1.49
2004–2005	1,751	27,656	15.79	3,609	2.06
2005–2006	3,439	35,288	10.26	3,714	1.08
2006–2007	4,328	61,981	14.32	3,023	0.70
2007–2008	4,232	44,268	10.46	1,833	0.43
Mean avg	3,095	37,434	12.25	2,951	1.15
S.D	1,285.68	16,792.92	2.61	776.35	0.65

Table 4. Rate of recovery of reportable finds by non-metal detectorists in England and Wales (derived from Portable Antiquities Scheme, 2004, p. 80 – Table 6, p. 87 – Table 13; 2005, p. 7, p. 101 – Table 8; 2006, p. 113 – Table 3a, p. 122 – Table 8; 2009, p. 267 – Table 2a, p. 277 – Table 7; 2010, p. 26 – Table 4a, p. 32 – Table 8)

Year	# of non-MD-reported finds	# of non-MD reporters	Non-MDs as percentage of reporters	Finds per non-MD per year
2003–2004	7,199	650	27.36	11.08
2004–2005	8,471	525	23.07	16.14
2005–2006	18,339	2,416	41.26	7.59
2006–2007	11,973	2,542	37.00	4.71
2007–2008	6,894	2,232	34.53	3.09
Mean avg	10,575	1,673	32.64	6.32
S.D	4,785.61	998.01	7.35	5.23
M. of error				4.59

Table 5. Proportion of metal detectorists who report finds in England and Wales (derived from Chitty & Edwards, 2004, p. 3; Portable Antiquities Scheme, 2004, p. 86 – Table 12; 2005, p. 100 – Table 7a, p. 100 – Table 7b; 2006, p. 120 – Table 7a, p. 121 – Table 7b; 2009, p. 274 – Table 7a, p. 275 – Table 7b; 2010, p. 14 – Table 1a, p. 15 – Table 1b)

Year	MDs who were contacted regularly by PAS	MDs who reported any finds to PAS	Percentage of regularly contacted MDs who reported any finds	Percentage of estimated total MDs who reported any finds
2003–2004	4,000	1,726	43.15	17.26
2004–2005	5,358	1,751	32.68	17.51
2005–2006	5,702	3,439	60.31	34.39
2006–2007	6,358	4,328	68.07	43.28
2007–2008	6,876	4,232	61.55	42.32
Mean avg	5,658.8	3,095.2	53.15	30.95
S.D	1,097.09	1,285.68	14.69	12.86
M. of error				11.27

Table 6. Low estimates of illicit metal detecting by population

Territory	Low estimate	Population at time	Scale by population
Austria	2,091	8,584,926	1 in 4,106
Ireland	1,128	4,640,703	1 in 4,114
Australia	5,119	23,781,169	1 in 4,646
Denmark	1,209	5,707,251	1 in 4,721
Canada	6,503	35,851,774	1 in 5,513
Belgium	1,680	11,285,721	1 in 6,718
Northern Ireland	225	1,851,600	1 in 8,229
New Zealand	348	4,595,700	1 in 13,206
England and Wales	3,500	54,809,100	1 in 15,660
Total	21,803	151,107,944	1 in 6,931

Table 7. Low estimates of illicit metal detecting by area (in square kilometres)

Territory	Low estimate	Territory in sq km	Scale by area
Belgium	1,680	30,528	1 in 18.17
Denmark	1,209	42,916	1 in 35.50
Austria	2,091	83,878	1 in 40.11
England and Wales	3,500	151,140	1 in 43.18
Ireland	1,128	70,283	1 in 62.31
Northern Ireland	225	14,130	1 in 62.80
New Zealand	348	268,000	1 in 770.11
Australia	5,119	7,692,000	1 in 1,502.64
Canada	6,503	9,984,670	1 in 1,535.39
Total	21,803	18,337,545	1 in 841.06

Table 8. Low estimates of licit metal detecting by population

Territory	Low estimate	Population at time	Scale by population
United States	1,562,500	306,771,529	1 in 196
England and Wales	24,397	57,885,400	1 in 2,373
Netherlands	5,353	16,936,520	1 in 3,164
Scotland	1,447	5,373,000	1 in 3,713
Denmark	1,385	5,707,251	1 in 4,121
Belgium	300	11,285,721	1 in 37,619
Total, including the United States	1,595,266	403,959,421	1 in 253
Total, excluding the United States	32,766	97,187,892	1 in 2,966

Table 9. Low estimates of licit metal detecting by area (in square kilometres)

Territory	Low estimate	Territory in sq km	Scale by area
United States	1,562,500	9,372,610	1 in 6.00
England and Wales	24,397	151,140	1 in 6.20
Netherlands	5,353	41,543	1 in 7.76
Denmark	1,385	42,916	1 in 30.99
Scotland	1,447	78,775	1 in 54.44
Belgium	300	30,528	1 in 101.76
Total, including the United States	1,595,266	9,717,512	1 in 6.09
Total, excluding the United States	32,766	344,902	1 in 10.53

Table 10. Low estimates of overall metal detecting by population

Territory	Low estimate	Population at time	Scale by population
United States	1,562,500	306,771,529	1 in 196
England and Wales	27,897	57,885,400	1 in 2,075
Denmark	2,594	5,707,251	1 in 2,200
Netherlands	5,353	16,936,520	1 in 3,164
Scotland	1,447	5,373,000	1 in 3,713
Austria	2,091	8,584,926	1 in 4,106
Ireland	1,128	4,640,703	1 in 4,114
Australia	5,119	23,781,169	1 in 4,646
Canada	6,503	35,851,774	1 in 5,513
Belgium	1,980	11,285,721	1 in 5,700
Northern Ireland	225	1,851,600	1 in 8,229
New Zealand	348	4,595,700	1 in 13,206
Total, including the United States	1,617,069	483,265,293	1 in 299
Total, excluding the United States	54,569	176,493,764	1 in 3,234

Table 11. Low estimates of overall metal detecting by area (in square kilometres)

Territory	Low estimate	Territory in sq km	Scale by area
England and Wales	27,897	151,140	1 in 5.42
United States	1,562,500	9,372,610	1 in 6.00
Netherlands	5,353	41,543	1 in 7.76
Belgium	1,980	30,528	1 in 15.42
Denmark	2,594	42,916	1 in 16.54
Austria	2,091	83,878	1 in 40.11
Scotland	1,447	78,775	1 in 54.44
Ireland	1,128	70,283	1 in 62.31
Northern Ireland	225	14,130	1 in 62.80
New Zealand	348	268,000	1 in 770.11
Australia	5,119	7,692,000	1 in 1,502.64
Canada	6,503	9,984,670	1 in 1,535.39
Total, including the United States	1,617,069	27,830,473	1 in 17.21
Total, excluding the United States	54,569	18,457,863	1 in 338.25

Table 12. Poll of hours of metal detecting per day in Austria (adapted from Karl, 2011, p. 121 – Figure 6)

Hours per day (HPD)	Number of metal detectorists (MDs)	Total
1–2	2	2
2–4	13	26
4–6	7	28
6+	2	12
Total	24	68
Minimum average HPD		2.83
Standard deviation		1.40
Margin of error		0.56

Table 13. Poll of days of metal detecting per year in Austria (adapted from Karl, 2011, p. 121 – Figure 7)

Days per year (DPY)	Number of metal detectorists (MDs)	Total
0–9	2	0
10–24	1	10
25–49	14	350
50+	7	350
Total	24	710
Minimum average DPY		29.58
Standard deviation		15.25
Margin of error		6.10

Table 14. Poll of hours of metal detecting per year in Denmark (adapted from Dobat & Jensen, 2016, p. 76 – Figure 5)

Hours per year (HPY)	Number of metal detectorists (MDs)	Total
0–10	5	0
10–50	10	100
50–100	18	900
100–500	84	8,400
500–1,000	34	17,000
1,000+	10	1,000
Total	161	36,400
Minimum average HPY		226.09
Standard deviation		264.06
Margin of error		40.79

Table 15. Minimum average hours of metal detecting per day in England and Wales (adapted from questionnaire survey by Robbins, 2012, v. 2, p. 16 – Figure 4.2)

Hours per day (HPD)	Number of metal detectorists (MDs)	Total
2	6	12
4	26	104
8	24	192
Total	56	308
Minimum average HPD		5.5
Standard deviation		2.26
Margin of error		0.59

Table 16. Minimum average days of metal detecting per week in England and Wales (adapted from questionnaire survey by Robbins, 2012 v. 2, p. 15 – Figure 4.1, v. 2, p. 20 – Table 4.2)

Days per week (DPW)	Number of metal detectorists (MDs)	Total
0.5	6	3
1	12	12
1	10	10
2	19	38
2	2	4
3–4	5	15
5–7	1	5
Total	55	87
Minimum average DPW		1.58
Standard deviation		0.86
Margin of error		0.23

Table 17. Minimum average days of metal detecting per year (adapted from Marc, 2004) and minimum average hours per year (according to the minimum average hours per day, as determined by the present analysis)

Days per year (DPY)	Number of metal detectorists (MDs)	Total person-days of detecting per year
3	36	108
36	127	4,572
52	110	5,720
104	291	30,264
365	60	21,900
Total	624	62,564
Minimum average DPY		100.26
Standard deviation		92.50
Margin of error		7.26
Minimum average HPY		298.78

Table 18. Netnographic survey of minimum average hours of metal detecting per day in principle (derived from Bigscoop, 2010; creative detecting, 2012; Crumble, 2016; Gorgar, 2012; Judy, 2008; Lifted Chevy, 2016; Marc, 2004; MetalDetectorDude, 2014; NjNyDigger, 2014; RaymondGrizzly, 2016; The dane, 2016; TreasureHunters, 2009; TripnBils, 2014)

HPD	MDs	Total
1	2	2
1–2	4	4
1–2.5	1	1
1–4	3	3
1–5	2	2
1.5	2	3
2	15	30
2–2.5	2	4
2–3	5	10
2–4	3	6
2–5	2	4
2–6	3	6
2–8	1	2
2.5	1	2.5
3	9	27
3–4	3	9
3–5	3	9
3–6	1	3
3.5	1	3.5
4	7	28
4–5	1	4
4–6	5	20
5	5	25
5–6	2	10
6	1	6
6–7	1	6
6–8	1	6
7.5–10	1	7.5
8–10	2	16
9–15	1	9
Total	90	268.5
Minimum average HPD		2.98
Standard deviation		1.70
Margin of error		0.35

Table 19. Netnographic survey of minimum average days of metal detecting per week in principle (derived from Bigscoop, 2010; creative detecting, 2012; Crumble, 2016; Gorgar, 2012; Judy, 2008; Lifted Chevy, 2016; Marc, 2004; MetalDetectorDude, 2014; NjNyDigger, 2014; RaymondGrizzly, 2016; The dane, 2016; TreasureHunters, 2009; TripnBils, 2014)

DPW	MDs	Total
0.25	1	0.25
0.5	4	2
0.75	1	0.75
0.75–1	1	0.75
1	35	35
1–2	3	3
1–4	1	1
2	22	44
2–3	10	20
3	31	93
3–4	7	21
3.5	1	3.5
4	6	24
4–5	5	20
4–6	1	4
5	1	5
5–6	5	25
5–7	1	5
6	2	12
7	24	168
Total	162	487.25
Minimum average DPW		3.01
Standard deviation		2.04
Margin of error		0.31

Table 20. Netnographic survey of minimum average hours of metal detecting per week in principle (derived from Bigscoop, 2010; creative detecting, 2012; Crumble, 2016; Gorgar, 2012; Judy, 2008; Lifted Chevy, 2016; Marc, 2004; MetalDetectorDude, 2014; NjNyDigger, 2014; RaymondGrizzly, 2016; The dane, 2016; TreasureHunters, 2009; TripnBils, 2014)

HPW	MDs	Total
0.5	1	0.5
0.75	1	0.75
0.75–1.5	1	0.75
1	2	2
1–1.5	1	1
1–2	1	1
1.33	1	1.33
2	1	2
2–3	1	2
2–4	1	2
2–6	1	2
2–12	1	2
2.5	1	2.5
3	2	6
3–4	2	6
3–5	2	6
3–6	1	3
4	4	16
4–5	2	8
4–6	3	12
4–18	1	4
5	2	10
5–6	2	10
5–10	1	5
6	2	12
6–8	1	6
6–9	1	6
6–15	1	6
6–20	1	6
7–28	1	7
8	4	32
8–10	4	32
8–18	2	16
9	2	18
9–12	1	9
9–30	1	9
10	5	50
10–12	2	20
10–20	1	10
10.5	1	10.5
12	2	24
12–14	2	24
12–15	1	12
12–18	1	12
12–20	2	24
12–24	1	12
14	2	28
14–20	1	14
14–21	1	14
14–35	1	14
15	3	45
15–17	1	15
15–20	3	45
16	1	16
16–30	1	16
17	1	17
20	3	60
20–24	1	20
20–30	1	20
21–28	1	21
21–35	1	21
24–36	1	24
25	1	25
30	1	30
45	1	45
Total	101	953.33
Minimum average HPW		9.44
Standard deviation		7.20
Margin of error		1.40

Table 21. Netnographic survey of minimum average hours of metal detecting per year in practice (derived from Bigscoop, 2010; creative detecting, 2012; Crumble, 2016; Gorgar, 2012; Judy, 2008; Lifted Chevy, 2016; Marc, 2004; MetalDetectorDude, 2014; NjNyDigger, 2014; RaymondGrizzly, 2016; The dane, 2016; TreasureHunters, 2009; TripnBils, 2014)

HPY	MDs	Total
24	1	24
36	1	36
36–72	1	36
48–72	1	48
52	2	104
52–104	1	52
70	1	70
104	1	104
104–156	1	104
104–208	1	104
104–312	1	104
104–624	1	104
130	1	130
156	2	312
156–208	2	312
156–234	1	156
156–260	2	312
156–312	1	156
208	4	832
208–260	2	416
208–312	3	624
208–936	1	208
240–260	1	240
260	1	260
260–312	1	260
260–520	1	260
300–360	1	300
312	2	624
312–416	1	312
312–468	1	312
312–780	1	312
338–364	1	338
351–585	1	351
364–606.67	1	364
364–1,248	1	364
365–1,460	1	365
416	3	1,248
416–520	4	1,664
416–936	2	832
468	2	936
468–624	1	468
494	1	494
520	5	2,600
520–624	2	1,040
520–1,040	1	520
547.5	1	547.5
624	1	624
624–728	2	1,248
624–780	1	624
624–1,040	1	624
693.33–832	1	693.33
728	1	728
728–1,040	1	728
728–1,820	1	728
730	1	730
730–1,095	1	730
780	3	2,340
780–884	1	780
780–1,040	3	2,340
832	1	832
832–1,560	1	832
884	1	884
1,040	3	3,120
1,040–1,560	1	1,040
1,092–1,456	1	1,092
1,095–1,460	1	1,095
1,248–1,872	1	1,248
1,300	1	1,300
1,560	2	3,120
1,937–2,119	1	1,937
Total	101	48,776.83
Standard deviation		369.43
Margin of error		72.05
Minimum average HPY		482.94
Minimum average HPM		40.24
Minimum average HPW		9.29

Table 22. Levels of metal detecting across months and seasons, as measured by reporting of finds in England and Wales (1st January 2003–31st December 2015, derived from Portable Antiquities Scheme, 2016)

Month	Finds	Season	Finds	Season’s % of year’s finds	% of peak season’s finds rate
March	176,801
April	118,193
May	72,899	Spring	367,893	33.77	100
June	91,416
July	63,381
August	88,463	Summer	243,260	22.33	66.12
September	90,348
October	84,632
November	85,350	Autumn	260,330	23.90	70.77
December	61,379
January	87,256
February	69,219	Winter	217,854	20.00	59.22
Total	1,089,337

Table 23. Minimum average number of reportable finds per detectorist per day and per hour (adapted from Robbins, 2012, v. 2, p. 36 – Table 4.4)

Number of reportable finds	Number of metal detectorists (MDs)	Total
1–2	39	39
3–4	10	30
5–6	2	10
7–8	1	7
11+	1	11
Total	53	97
Standard deviation		1.82
Margin of error		0.49
Minimum average of RFPD		1.83
Minimum average RFPH		0.31

Table 24. Minimum average number of material finds per detectorist per day and per hour (adapted from Robbins, 2012, v. 2, p. 36 – Table 4.4)

Total number of finds	Number of metal detectorists (MDs)	Total
0–9	27	0
10–19	21	210
20–29	5	100
40–49	1	40
Total	54	350
Standard deviation		8.05
Margin of error		2.15
Minimum average of MFPD		6.48
Minimum average of MFPH		1.10

Table 25. Comparison of polls and surveys on hours per detectorist per year

Territory	Source	Number of MDs	Min avg HPY
UK	Survey (Robbins, 2012)	55	452.40
International	Poll (Marc, 2004)	624	298.78
International	Netnography	101	286.02
Denmark	Poll (Dobat & Jensen, 2016)	156	226.09
Austria	Survey (Achleitner, 2011)	133	218.40
Austria	Survey (Karl, 2011)	24	83.71

Table 26. Estimates of minimum average person-hours of illicit detecting per year, number of reportable finds per year and total number of material finds per year, ranked by quantity

Territory	Low estimate	Min avg person-hours per year	Min avg number of reportable finds per year	Total number of material finds per year
Canada	6,503	1,859,988	576,596	2,045,987
Australia	5,119	1,464,136	453,882	1,610,550
England and Wales	3,500	1,001,070	310,332	1,101,177
Austria	2,091	598,068	185,401	657,875
Belgium	1,680	480,514	148,959	528,565
Denmark	1,209	345,798	107,197	380,378
Ireland	1,128	322,631	100,015	354,894
New Zealand	348	99,535	30,856	109,488
Northern Ireland	225	64,355	19,950	70,790
Total	21,803	6,236,094	1,933,189	6,859,703

Table 27. Estimates of minimum average person-hours of licit detecting per year, number of reportable finds per year and total number of material finds per year, ranked by quantity

Territory	Low estimate	Minimum average person-hours per year	Minimum average number of reportable finds per year	Total number of material finds per year
United States	1,562,500	446,906,250	138,540,938	491,596,875
England and Wales	24,397	6,978,030	2,163,189	7,675,833
Netherlands	5,353	1,531,065	474,630	1,684,172
Denmark	1,385	396,138	122,803	435,751
Scotland	1,447	413,871	128,300	455,258
Belgium	300	85,806	26,600	94,387
Total, including the United States	1,595,266	456,277,981	141,446,174	501,905,779
Total, excluding the United States	32,766	9,371,731	2,905,237	10,308,904

Table 28. Estimates of minimum average person-hours of overall detecting per year, number of reportable finds per year and total number of material finds per year, ranked by quantity

Territory	Low estimate	Minimum average person-hours per year	Minimum average number of reportable finds per year	Total number of material finds per year
United States	1,562,500	446,906,250	138,540,938	491,596,875
England and Wales	27,897	7,979,100	2,473,521	8,777,010
Canada	6,503	1,859,988	576,596	2,045,987
Netherlands	5,353	1,531,065	474,630	1,684,172
Australia	5,119	1,464,136	453,882	1,610,550
Denmark	2,594	741,936	230,000	816,129
Austria	2,091	598,068	185,401	657,875
Belgium	1,980	566,320	175,559	622,952
Scotland	1,447	413,871	128,300	455,258
Ireland	1,128	322,631	100,015	354,894
New Zealand	348	99,535	30,856	109,488
Northern Ireland	225	64,355	19,950	70,790
Total, including the United States	1,617,069	462,514,075	143,379,363	508,765,483
Total, excluding the United States	54,569	15,607,825	4,838,426	17,168,608

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