Registration in the Danish Regional Nonmelanoma Skin Cancer Dermatology Database: completeness of registration and accuracy of key variables

Figures & data

Table 4 Formulae to calculate the PPV, NPV, and sensitivity and specificity

	NMSC database	Medical record review
		yes	no
eg, First skin cancer ever	Yes	a	b	PPV = a/(a + b)
	No	c	d	NPV = c/(c + d)
		Sensitivity = a/(a + c)	Specificity = b/(b + d)

Notes: PPV, positive predictive value. The proportion of patients registered with ‘yes’ for a given variable in the database confirmed in the medical record (ie, the variable: diagnosis, according to the DPR) for variables: ‘diagnosis overall’, ‘treatment overall’, ‘size’, localization’ and ‘treatment date’ PPVs were the proportion of a given variable registered in the database confirmed in the medical record/DPR; NMSC, nonmelanoma skin cancer; NPV, The proportion of patients registered with ‘no’ for a given variable in the database confirmed in the medical record (ie, the variable; diagnosis, according to the DPR); Sensitivity, The proportion of patients registered with ‘yes’ for a given variable in the medical record, who were registered with a ‘yes’ in the database (ie, the variable diagnosis, according to the DPR); Specificity, The proportion of patients with ‘no’ for a given variable in the medical record, who were registered with a ‘no’ in the database (ie, the variable diagnosis, according to the DPR).

Abbreviations: DPR, Danish Pathology Registry; NMSC, nonmelanoma skin cancer; NPV, negative predicted value; PPV, positive predicture value.

Table 1 Descriptions of patients and tumors in the nonmelanoma skin cancer database

	Registration from Jan 1 2008 – Aug 31 2009 in the NMSC database (%)	Study population for calculation of completeness: Registration from Jan 1 – Jun 30 2008 (%)	Medical record reviews used to calculate PPV and completeness (%)
Total numbers of patients	1,775	288	67
Male	892 (50)	136 (47)	31 (46)
Female	883 (50)	152 (53)	36 (54)
Clinics
Clinic no 1	457	178 (62)	39 (58)
Clinic no 2	296	110 (38)	28 (42)
Age < 55	264 (15)	49 (17)	16 (24)
Age ≥ 55 and <75	889 (50)	154 (53)	29 (43)
Age ≥ 75	622 (35)	85 (30)	22 (33)
History of previous skin cancer
No history of skin cancer	992 (56)	156 (54)	32 (48)
History of previous skin cancer	737 (42)	130 (45)	34 (51)
Unknown	45 (3)	2 (1)	1 (2)
Missing	1 (–)	0	0
Total numbers of tumors	2,400	359	78
Histological diagnosis
Basal cell carcinoma	2,090 (87)	328 (91)	72 (92)
Squamous cell carcinoma	123 (5)	10 (3)	2 (3)
Mb. Bowen	77 (3)	9 (3)	2 (3)
Keratoacanthoma	34 (1)	7 (2)	2 (3)
Keratoacanthoma/SCC	1 (–)	1 (–)	0
No pathology test performed	57 (2)	4 (1)	0
Histology inconclusive	10 (–)	0	0
Missing histology registration	8 (–)	0	0
Tumor registered is
A new primary tumor	2,173(91)	324 (90)	69 (88)
A previously treated tumor	221 (9)	35 (10)	9 (12)
Missing	6 (–)	–	–
Treatment modality
Curettage with or without cautery	1,919 (80)	294 (82)	65 (83)
Cryotherapy	38 (2)	3 (1)	0
Excision	157 (7)	9 (3)	1 (1)
Tangential excision with or without curettage	4 (–)	1 (–)	0
Photodynamic therapy	55 (2)	15 (4)	1 (1)
Imiquimod	42 (2)		1 (1)
Referred to hospital treatment	152 (6)	28 (8)	9 (11)
No treatment	17 (–)	1 (–)	0
Treatment variable missing	16 (1)	6 (2)	1 (1)

Abbreviations: PPV, positive predictive value; SCC, squamous cell carcinoma.

Table 2 Completeness of registration of patients in the nonmelanoma skin cancer database

	Patients registered in database (no.)	Patients registered in the DPR (no.)	Degree of completeness (Evaluation: DPR) % (95% CI)	Patients registered in database (no.)	Patients registered in the medical records (no.)	Degree of completeness (Evaluation: medical records) % (95% CI)
Overall patients	288	452	62 (58–67)	67	88	76 (66–85)
Completeness for each clinic
Patients clinic no 1	178	182^a	93 (88–94)	39	41	95 (84–99)
Patients clinic no 2	110	270^b	40 (34–46)	28	47	60 (44–74)

Abbreviations: CI, confidence interval; DPR, Danish Pathology Registry.

Table 3 Completeness of follow-up visit registration in the nonmelanoma skin cancer database

	1st follow-up visit (<6 months after treatment)				2nd follow-up visit (6–15 months after treatment)
	Patients registered in the database (no.)	Follow-up visit registered in database (no. of patients)	Follow-up visits registered in medical records (no.)	Degree of completeness of 1st follow-up visits: % (95% CI)	Patients registered in the database (no.)	Follow-up visit registered in database. (no. of patients)	Follow-up visits registered in medical records (no. of patients)	Degree of completeness of 1st follow-up visits: % (95% CI)
Overall	54	39	46	85 (71–94)	54	24	36	67 (49–81)
Clinic no 1	29	22	22	100 (85–100)	29	14	19	74 (49–91)
Clinic no 2	25	17	24	71 (49–87)	25	10	17	59 (33–82)

Abbreviation: CI, confidence interval.

Table 5 Validity of variables registered in the nonmelanoma skin cancer database. Verified in medical records

	NMSC database	Medical record		Total	PPV % (95% CI)	NPV % (95% CI)	Sensitivity % (95% CI)	Specificity % (95% CI)
		yes	no
Histological diagnosis overall	Total	78*	0	78	78/78 = 100 (95–100)
Basal cell carcinoma	Yes	72	0	72	72/72 = 100 (95.0–100)	6/6 = 100 (54–100)	72/72 = 100 (95–100)	6/6 = 100 (54–100)
Squamous cell carcinoma	Yes	2	0	2	2/2 = 100 (15.8–100)	76/76 = 100 (95–100)	2/2 = 100 (15.8–100)	76/76 = 100 (95–100)
Mb. Bowen	Yes	2	0	2	2/2 = 100 (15.8–100)	76/76 = 100 (95–100)	2/2 = 100 (15.8–100)	76/76 = 100 (95–100)
Keratoacanthoma	Yes	2	0	2	2/2 = 100 (15.8–100)	76/76 = 100 (95–100)	2/2 = 100 (15.8–100)	76/76 = 100 (95–100)

Notes: Histological diagnosis confirmed in the medical record.

Abbreviations: CI, confidence interval; PPV, positive predictive value. NPV, negative predictive value.

Table 6 Validity of variables registered in the nonmelanoma skin cancer database. Verified in medical records

	NMSC database:	Medical record		Total	Missing	PPV % (95% CI)	NPV % (95% CI)	Sensitivity % (95% CI)	Specificity % (95% CI)
		Yes	No
First skin cancer ever (incident case)	Yes	31	1	32		31/32 = 97 (85–100)		31/33 = 97 (85–100)
	No	2	32	34			32/34 = 94 (80–99)		32/34 = 94 (80–99)
	Unknown		1
	Total	33	34
Tumor registered is a new primary tumor	Yes	67	1	68	1	67/68 = 99 (92–100)		67/67 = 100 (95–100)
	No	0	9	9			9/9 = 100 (66–100)		9/10 = 90 (55–100)
	Total	67	10
Localization of tumor		75^*	3^*	78		75/78 = 96 (89–99)
Size		29^*	5^*	34	44	29/34 = 85 (69–95)
Treatment date		71^*	7^*	78		71/78 = 91 (82–96)
Treatment modality overall	Total	73^*	4^*	77		73/77 = 95 (87–99)
	missing				1
Curettage ± cautery	Yes	62	3	65		62/65 = 95 (87–99)		62/63 = 98 (91–100)
	No	1	11	12			11/12 = 92 (62–100)		11/14 = 79 (49–95)
	Total	63	14
Other treatments incl. excision, photodynamic therapy, imiquimod creme	Yes	2	1	3		2/3 = 67 (9–99)		2/4 = 50 (7–93)
	No	2	72	74			72/74 = 97 (91–100)		72/73 = 99 (93–100)
	Total	4	73
Referred to hospital treatment	Yes	9	0	9		9/9 = 100 (66–100)		9/9 = 100 (66–100)
	No	0	68	68			68/68 = 100 (95–100)		68/68 = 100 (95–100)
	Total	9	68
Recurrence at 1st or 2nd follow-up visit	Yes	3	0	3		3/3 = 100 (29–100)		3/4 = 75 (19–99)
	No	1	43	44			43/44 = 98 (88–99)		43/43 = 100 (92–100)
	Total	4	43		3
	missing	4	11
Complications in relation to treatment	Yes	2	0	2		2/2 = 100 (16–10)		2/3 = 67 (9–99)
	No	1	51	52			51/52 = 98 (90–100)		51/51 = 100 (93–100)
	Total	3	51
	missing	0	8		3

Notes: Confirmed in medical record (yes/no).

Abbreviations: CI, confidence interval; NPV, Negative predictive value; PPV, Positive predictive value.