Evaluation of the coverage of the linked Canadian 

Community Health Survey and hospital inpatient records 

Michelle Rotermann and Claude Nadeau 

Statistics Canada

Michelle.Rotermann@statcan.ca Claude.Nadeau@statcan.ca

Abstract

Rationale: The Longitudinal Health and Administrative Data Initiative is a joint project between

the provincial Ministries of Health and Statistics Canada. One objective of the Initiative is to

address information gaps through research linking person-oriented hospital inpatient (HPOI) and

survey data. Evaluation of the coverage as a result of the linkage between theses data sources is

an important preliminary step before engaging in further analyses based on the linked file. 

Methods: To evaluate the coverage of the linkage between the Canadian Community Health

Survey (CCHS) and HPOI, the number of individuals admitted to hospital according to each 

source was compared. CCHS respondents were considered to have been hospitalized if a record

containing similar demographic characteristics and/or health number (HN), and an admission to an

acute-care facility between September 2000 and November 2001 was found in HPOI. Survey 

weights were applied to these records to calculate the estimated number of individuals 

hospitalized. Because HPOI is a virtual census of hospital admissions, it was regarded as the 

standard; differences between HPOI and weighted CCHS counts indicated possible linkage failure 

and undercoverage. Quebec records were excluded because the HNs in HPOI are scrambled and 

other linking variables are not provided/incomplete. Results: According to HPOI for September 

2000 - November 2001, 1,612,269 Canadians were hospitalized. Weighted estimates from the 

CCHS adjusted for agreement to link and agreement and plausible HN were lower (17% and 10%,

respectively). The under-coverage rates were similar between men and women; lower among 

persons living in Manitoba than the rest of Canada; higher among individuals aged 12-74 than 

among those aged 75+. Conclusion: The number of Canadians (outside Quebec) aged 12+ who 

were hospitalized, based on HPOI, was higher than the number based on CCHS-HPOI linkage. 

The discrepancy varied by province/territory and age; therefore, use of the linked file could lead to

biased estimates. Nevertheless, the coverage as a result of the linkage was acceptable and use of 

the file for population-based research is encouraged. 

Introduction 

The Longitudinal Health and Administrative Data (LHAD) Initiative is a project between the provincial 

Ministries of Health and Statistics Canada (STC). One objective of the initiative is to address health

information gaps through research combining individual-level administrative health care records, vital

events data, such as cause and date of death, the cancer registry and information from STC’s general health

surveys. This research will provide pan-Canadian and comparative information across provinces and will 

improve understanding of the relationships between risk factors, socio-economic characteristics, health

status measures and health care system utilization.

Initial research on the rate of linkage between CCHS and HPOI quantified the proportion of CCHS survey 

respondents who had been hospitalized during the 1994/95-2004/05 period, but coverage of the linkage was 

not assessed (Nadeau C, Beaudet MP, Marion J; 2006). Evaluation of the coverage as a result of the

linkage between person-level inpatient hospitalization data (HPOI) and survey data is an important

preliminary step before engaging in further analyses based on the linked file. 

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Background 

Health care service data such as hospital discharges are collected as part of the billing and payment process 

of each province and territory. Though the data were not initially collected for research, these data are

successfully used to describe the quantity and quality of health care services and health outcomes of 

inpatients (Rotermann M, 2004; Johansen H, Nair C, Mao L et al, 2002; Wray NP, Ashton CM, Kuykendall

DH et al. 1995). 

Administrative hospital discharge records are a viable source of information about inpatient hospital stays 

but do not include information about services provided on an outpatient basis, including services received 

via the emergency department or day surgeries. Currently, deaths occurring outside of hospital are not

routinely linked with hospitalization data. Hospital discharge records also provide limited information

about the non-medical determinants of health, such as socio-economic status and behavioural/lifestyle 

factors, for example smoking status or body mass index (BMI). In contrast, STC’s health surveys are a rich

source of information about health status, determinants of health and to a lesser extent health care service 

use.

Combining micro-level administrative data with STC's data holdings can minimize many of the limitations

inherent in each individual data source, thereby facilitating a more complete understanding of how 

individuals fare in their contacts with the health care system. 

Methods 

Data sources 

Canadian Community Health Survey

The CCHS is a cross-sectional survey that collects information related to health status, health care 

utilization and health determinants for the Canadian population. It covers the household population aged

12 or older in all provinces and territories, except members of the regular Forces and residents of

institutions, Indian reserves, and some remote areas (approximately 98% of the population). Data for cycle 

1.1 were collected between September 1, 2000 and November 3, 2001 from a sample of 131,535 persons 

and the response rate was 84.7%. The vast majority of the respondents (90.8%; 119,383) gave permission

to link their survey records with administrative health records and about three-quarters provided a valid HN 

(73.1%; 87,268). More information about the CCHS is available in a published report (Béland, 2002). 

The sample used for this study consists of 98,450 respondents aged 12+ in all provinces and territories 

except Quebec.

In order for estimates produced from survey data to be representative of the target population, and not just

the sample itself, survey weights were used. Generally survey weights reflect the differing probabilities of 

selection and differential response rates. The survey weight is the number of persons in the population 

represented by each survey respondent. Each record is therefore weighted by the inverse of the probability 

of selecting the person and getting a response from him or her. 

With record linkage additional survey weights are required because not all survey respondents agree to link 

and not all respondents who agree to link provide a valid HN. For this study, two sets of survey weights 

specifically designed for record linkage were derived. The first set adjusted for respondents who agreed to

have their survey data linked to their administrative health records; the second set adjusted for agreement to

link and HN validity. 

Currently, STC does not have access to jurisdictional population registries which would provide a means of 

verifying the HNs provided by the respondent. Instead all provinces provide check-digit formulas which 

are used to verify that the HNs provided by the respondents are at least plausible. Check-digits are not a 

substitute for registries which would provide first and last names, birth dates, addresses and HNs but they 

can detect accidental transcription errors, such as the inversion of two numbers and provide a simple 

method of distinguishing meaningful numbers from strings of random digits. 

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Health person-oriented information database (HPOI)

 

 

 

 

The territories did not provide a check-digit. As a result HN length and other known characteristics of the 

number, such as expected first alpha or numeric were used to assess HN plausibility. 

Table 1: Number of Canadian Community Health Survey respondents who agreed to have 

their survey responses linked with their administrative health records and the proportion 

who provided a valid health number, by selected characteristics, Canada excluding Quebec, 

2001 

Agreed to link Agreed to linkage and provided valid HN 

Unweighted % Unweighted % 

Total 98,450 90.4 72,671 73.8 

Province/territories 

NF 3,533 90.3 3,037 86.0 

PE 3,238 88.7 2,236 69.1 

NS 4,938 92.8 4,109 83.2 

NB 4,634 92.8 3,746 80.8 

ON 35,674 90.8 24,917 69.8 

MB 7,653 90.4 5,692 74.4 

SK 7,417 92.6 6,142 82.8 

AB 12,757 88.3 9,156 71.8 

BC 16,493 90.1 11,991 72.7 

YK 633 78.2 439 69.4 

NT 882 88.1 701 79.5 

NU 598 84.6 505 84.4 

Sex 

Males 45,585 90.3 32,202 70.6 

Females 52,865 90.5 40,469 76.6 

Age groups

12-24 19,246 91.8 13,592 70.6 

25-34 14,482 90.9 10,162 70.2 

35-44 18,892 90.2 13,942 73.8 

45-54 16,036 89.6 11,968 74.6 

55-64 11,493 90.0 8,732 76.0 

65-74 9,778 90.3 7,713 78.9 

75+ 8,523 89.5 6,562 77.0 

12-74 89,927 90.5 66,109 73.5 

Data source: Canadian Community Health Survey, 2001 

Note: CCHS respondents were asked if Statistics Canada had their permission to link information collected during 

the interview with provincial health information, including information on past and continuing use of services such 

as hospitals, clinics, doctor's offices or other services provided by the province was determined by answering the 

following question. HN validity was assessed using a provincially provided check-digit formula. HN length and 

other known characteristics of a particular jurisdiction's HN were used in the absence of a check-digit.

The Health Person-Oriented Information (HPOI) Database, maintained by Statistics Canada, contains

information on inpatient hospital separations (discharges and in-hospital deaths) and is composed of 

hospital discharge abstracts from virtually all acute-care, and some psychiatric, chronic and rehabilitative 

hospitals across Canada. Data are available for all provinces and the Northwest Territory from fiscal year 

1994/1995 onwards; data for 1992/1993 and 1993/1994 are available for some provinces. Although the 

HPOI database includes all records from the Hospital Morbidity Database (HMDB), not all records can be 

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submitted to the person-oriented linkage process. Annually, approximately 13% of the HMDB records are 

excluded from the additional processing that enables the files to be analyzed at the person level: 10% 

because they are records for newborns and the remaining 3% because the record contains either an invalid 

identifier (HN) or is for a person residing outside the province. 

During the linkage process, records belonging to the same individual are identified by means of the 

patient’s health number (HN). A critical part of the process is to determine if more than one person is 

using the same HN (e.g. spouses, mother and child). Other data elements in the HMDB (e.g., sex and birth 

date) can be used to differentiate among individuals using the same HN. Unlike the HMDB which is eventbased, HPOI is a person-oriented database that allows for longitudinal analysis of inpatient hospitalizations. 

Each record contains demographic (for example, postal code, date of birth), non-medical administrative 

(such as health number, dates of admission and separation) and clinical information (for example, 

diagnoses and procedures). 

Over the 14 months studied (September 1, 2000-November 3, 2001), there were 2.3 million hospital 

discharges of 1,612,269 individuals aged 12+ from acute-care hospitals, outside Quebec. Admissions to

non-acute hospitals were excluded because coverage of other hospital types varied by province. 

Quebec records excluded 

Quebec HPOI records cannot be linked to CCHS survey records because the Quebec HPOI records 

provided to Statistics Canada contain scrambled health numbers (HNs), no date of birth and incomplete

postal codes. 

Analytical techniques 

To evaluate the coverage of Cycle 1.1 of the CCHS and HPOI, the number of individuals admitted to

hospital according to each data source was compared (an approach that has not been used before). 

Probabilistic linkage was used to identify CCHS respondents who were hospitalized. Generalized Record

Linkage software (GRLS) developed at Statistics Canada was used to execute the linkage. 

Record linkage is a process of bringing together two or more separately recorded pieces of information 

belonging to the same entity. By combining datasets, new information is learned because each dataset 

contains some information not available in the other (Winglee M, Valliant R, Scheuren F 2005). The two 

data sources linked for this study contained many variables –HPOI has more than 100; CCHS has more

than 1000, but only a few fields appeared in both and were unique enough to be useful as matching fields

for linkage. A CCHS respondent was considered to have been hospitalized if a record containing similar 

demographic characteristics (for example, birth date, sex, postal code) and/or HN, and an admission date to

an acute-care facility between September 1, 2000 and November 3, 2001 was found in the HPOI database. 

Probabilistic linkage does not require complete agreement on the matching variables. Instead the quality of

the match between pairs of records is rated using sophisticated algorithms to evaluate the likelihood of a 

correct match between two records (Fellegi and Sunter 1969). Points are given or subtracted depending on

the similarity between fields. The higher the score, the more likely the two records pertain to the same

individual. Point values are chosen in various ways, including through probabilities, hence the name

probabilistic linkage. For this study, high positive scores were assigned if the HNs were identical between 

two records and the issuing province matched; if the values were similar but not exact, according to a string 

comparison algorithm, a lower positive score was assigned, reflecting partial agreement; if the values on

the two records were totally different, points were subtracted. The number of points assigned to each pair

reflected the importance of the matching variable, which was usually related to its uniqueness. Total 

linkage weights for each pair of CCHS-HPOI records were calculated by summing the scores assigned to

each pair of linking variables, including HN, postal code, sex, and date of birth. 

Total linkage weights optimally form a bi-modal distribution. Typically pairs of records which score above

a selected upper threshold are accepted as “true” matches; pairs below are rejected; pairs between the

selected cut-offs are considered potential matches and require manual intervention. To minimize the 

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A ON 11/06/1964 L9Y3B9 3512345678 

1 ON 11/06/1964 L9Y3B9 3512345678 

F MB 24/07/1927 R0A0T0 55667788 

1 ON 11/06/1964 L9Y3B9 3512345678 

B MB 21/05/1945 R0A0T0

7 MB 21/05/1945 R0A0T0 4624252627 

B MB 21/05/1945 R0A0T0

1 ON 11/06/1964 L9Y3B9 3512345678 

amount of manual review the cut-off points chosen for this study were identical which meant that scored

pairs could only take one of two values: match or non-match. Pairs with scores greater than or equal to

250 were considered to be matches; pairs below were considered to be non-matches. 

Chart 1: Example of how pairs of records were assessed and scored using Generalized Record Linkage 

Software (GRLS) 

Id Prov Birthdate Postal 

code HN Sex 

Score 

calculated 

by GRLS 

Match? Commentary

F 

F 

447 Y All fields match 

M 

F 

-308 N Nothing matches 

- M 

M 

268 Y 

HN missing; 

everything else

matches

- M 

F 

-244 N

HN missing; 

nothing else 

matches

CCHS record HPOI record 

To calculate the number of individuals hospitalized using CCHS two sets of survey weights were applied to

the records of CCHS respondents for whom records were also found in the HPOI database. The first set

was adjusted for agreement to link (8,216); the second was adjusted for agreement to link and HN validity 

(6,810). Two coverage rates were calculated by dividing each set of weighted CCHS estimates by hospital

inpatient counts and then multiplying by 100%. Because HPOI is a virtual census of hospital admissions, 

the count of hospitalizations from HPOI was regarded as the standard; the difference between the HPOI 

count and each weighted count from the CCHS was examined. Standard errors and 95% confidence 

intervals were calculated using the bootstrap technique. Statistical significance was tested using the t-test 

(p<0.05). 

Limitations 

Coverage of the data sources is not exactly the same. For example, CCHS excludes institutionalized

persons; HPOI is a virtual census of acute-care hospitalizations. The inclusion of seniors will help us to

quantify the extent of missed hospitalization attributable to institutionalized seniors. Quebec was excluded

from the analysis because the HNs of Quebec residents are scrambled and other identifying information is

not provided to Statistics Canada. Individuals under age 12 were excluded because the target population of

the CCHS (.1 cycles) covers only the 12+ population. Linkage of Manitoba CCHS records with HPOI was 

compromised by the collection of incomplete birth dates and the provision of family rather than personal 

HNs (Manitoba residents have both). Probabilistic linkage results in some false links and misses some true

links. Both types of errors may have occurred in this study. Intra-provincial and inter-provincial mobility

may have also lowered the number of links, although the effect of mobility on the linkage is believed to

have been minimized by restricting the study period to hospitalizations occurring in the same 14 monthperiod overlapping with the CCHS collection. Mobility within a province would have less of an effect on

linkage than a move to another province. Moves within a province would only change the postal code, 

whereas a move to another province/territory may also change the HN since it is provincially/territorially 

assigned and non-transferable across provinces. 

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Canada‡1,612,269 8,216 1,333,478 6,810 1,450,211 82.7 

Findings

According to HPOI, between September 1, 2000 and November 3, 2001, 1,612,269 Canadians were

admitted to an acute-care hospital (excluding Quebec). Weighted estimates from the CCHS adjusted for 

agreement to link or agreement and valid HN were lower (1,333,478 and 1,450,211, respectively). 

Regardless of which CCHS estimate was used, coverage rates were similar between men and women;

lower among persons living in Manitoba (68.9 % and 78.1%) than the rest of Canada; higher among 

individuals aged 12-74 (86.0% and 94.2%) than among those aged 75+ (70.2% and 73.5%). While the 

coverage rates for the territories are relatively high, the small number of CCHS records linked to HPOI

precludes any analysis featuring jurisdictional comparisons. 

Table 2: Number hospitalized in acute-care hospitals, September 1, 2000-November 3, 2001, aged 12+, Canada 

excluding Quebec, by province/territory and data source 

Health person-oriented 

information (HPOI) 

Count (N) 

Province/territory 

NF 41,455 

PE 11,840 

NS 68,109 

NB 68,099 

ON 760,982 

MB 88,305 

SK 88,571 

AB 210,192 

BC 268,876 

YK 1,830 

NT 3,015 

NU 995 

Sex 

Females†

996,926 

Males 615,337 

Age group 

12-24 180,655 

25-34 282,609 

35-44 215,326 

45-54 187,202 

55-64 183,314 

65-74 229,522 

75+ 333,641 

12-74†

1,278,628 

Canadian Community Health Survey (CCHS) 

Weights adjusted for: 

Agreed to linkage and 

Agreed to linkage provided valid HN 

Unweighted Weighted Weighted (N) Unweighted (n) (n) (N) 

309 37,430 278 39,769 

298 10,155 237 11,071 

407 56,650 350 60,799 

480 57,839 424 62,487 

2,843 635,679 2,230 694,240 

672 60,877 581 68,985 

752 77,338 660 78,755 

1,054 171,149 862 185,899 

1,255 220,773 1,060 241,838 

48 1,827 37 1,992 

77 2,884 70 3,323 

21 878 21 1,051 

5,241 843,973 4,356 904,061 

2,975 489,504 2,454 546,150 

897 155,850 718 165,050 

1,258 242,187 1,047 274,388 

1,003 185,754 826 205,475 

932 159,856 779 175,734 

1,026 156,849 854 165,678 

1,274 198,716 1,089 218,733 

1,825 234,267 1,497 245,154 

7,318 1,099,212 6,810 1,205,058 

Coverage rates 

Agreed to 

linkage 

Agreed and 

to provided 

linkage valid HN 

% % 

89.9 

90.3 95.9 

85.8 93.5 

83.2 89.3 

84.9 91.8 

83.5 91.2 

68.9* 78.1* 

87.3 88.9 

81.4 88.4 

82.1 89.9 

99.8 108.9 

95.7 110.2* 

88.2 105.6 

84.7 90.7 

79.6 88.8 

86.3 91.4 

85.7 97.1 

86.3 95.4 

85.4 93.9 

85.6 90.4 

86.6 95.3 

70.2* 73.5* 

86.0 94.2 

‡ Reference category is Canada minus each province (Rest of Canada) † Reference category 

* Significantly different from reference category (p<0.05). 

Data source: Canadian Community Health Survey, 2001 and Health person-oriented information 2000/01-2001/02 

Notes: Counts, linkage and coverage rates as of July 31, 2007; counts, linkage and coverage rates may change pending final revision.

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Conclusion 

The value of record linkage is now a well-established technique in epidemiological studies of population 

health. By linking information from routinely collected administrative health data files with survey data 

already available at STC much can be learned about the health determinants, different types of health care 

utilization and health outcomes. Because the survey data are population-based the information to be

learned will be generalizable to the household population of Canada, with few exceptions. 

Coverage evaluation is a fundamental pre-requisite to further analyses based on the CCHS-HPOI linked 

file. The number of Canadians (outside Quebec) aged 12+ who were hospitalized, based on HPOI, was 

higher than the number based on the CCHS-HPOI linkage. The discrepancy varied by province/territory

and age. Therefore, use of the linked file could lead to bias. For example, because the coverage rate of 

persons over the age of 75 is relatively low, use of the linked file underestimates hospitalization in this age 

group. Nevertheless, the overall estimates produced as a result of this linkage are of an acceptable level. 

Future research using this linked file is encouraged, bearing in mind the aforementioned limitations.

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