Data received from the Clinical Practice Research Datalink

Initial test data set received 10 May 2013.

First baseline data set received 19 December 2013.

Second baseline data set received 3 February 2014.

Third baseline data set received 13 July 2014.

Baseline and follow-up data set received 19 January 2015.

Clinical Practice Research Datalink data

Data from the consultation, clinical, immunisation, test, referral and therapy tables from the CPRD Gold Data dictionary were used.

Overview

Figure 26 shows a very broad overview of how the data have been processed and the number of records. Full details of assumptions are now described.

FIGURE 26

Decision tree showing an overview of how medical contacts have been allocated.

General assumptions

One ‘consultation’ (based on the combination of patient ID, practice ID and consultation ID) in the consultation table is considered one contact.

All consultation data supplied, not just those that are asthma related, are taken into account for the study.

Only consultations that happened on or after 1 August 2012 are included.

Assumptions used to code records as scheduled or unscheduled (contact type) are based on clinical, immunisation, therapy, referral, test and consultation data.

Records with unmatched event dates

Each consultation record is supplied with an event date; this event date does not always match the event date recorded for that consultation within the other tables. This is most likely a result of information entered into the database historically. Those contacts within the clinical table were included if they were relevant and unlikely to be duplicated (see Inclusion of ‘unmatched/historical’ data section for more details). All immunisation, therapy, referral and test records that did not match the event date supplied in the consultation data were excluded.

Clinical data

Clinical data are linked to consultation data, and all matched records are included.

Inclusion of ‘unmatched/historical’ data

If the event date does not match but the clinical event date is within the dates of interest (i.e. from 1 August 2012 to 30 September 2014), then those records that are both relevant and unlikely to be duplicated are included. The decision on which records to include was made by the GP Adjudication Panel after reviewing the most common unique terms (10% of the terms, which covered 88% of the data). The most common 10 terms and the decision of whether or not to include them is shown in Table 25 for information; rules based on this review were used to decide whether or not to include the 12% of data not reviewed, for example ‘if it contains seen it is relevant and unlikely to be duplicated’.

TABLE 25

Inclusion of ‘unmatched/historical’ data

Summary of coding using clinical data

The records included are used to determine scheduled or unscheduled contacts based on ‘medcode description’; the clinical data references Pegasus medical data using the field ‘medcode’ to get ‘medcode description’. If contact types cannot be determined by ‘medcode description’, then clinical consultation type ‘constype’ (consultation type) is referenced.

Following GP Adjudication Panel review of the medcode descriptions, in which over 90% of the data were reviewed (17% of the unique terms), clinical records to be marked as scheduled, unscheduled, not applicable or unknown were identified based on terms (see Boxes 1–4 and Tables 26 and 27 for examples; full details are available on request). Based on this review, rules to apply to the data were also determined (see Table 26). Finally, decisions on how to code the remaining records based on the clinical consultation type were made (see Table 27).

BOX 1

Clinical records: scheduled

BOX 4

Clinical records: unknown

TABLE 26

Medcode description rules coding

TABLE 27

Clinical consultation type coding

BOX 2

Clinical records: unscheduled

BOX 3

Clinical records: not applicable

Conflicting clinical contact types

Clinical data contain more than one record per consultation. In some cases, the same consultation ID can have more than one clinical contact type. For these clinical records, we assume that unscheduled takes precedence (i.e. they are likely to have come in for an unscheduled visit but had a scheduled ‘type’ of procedure at the same time) over all other contact types; that scheduled takes precedence over not applicable and unknown; and that unknown takes precedence over not applicable.

Clinical to consultation

The code assigned in accordance with clinical contact type as described above is linked to the consultation data.

Consultation data marked as ‘unknown’ based on the clinical data as well as consultation data that did not link to clinical data are coded based on immunisation, therapy, referral, test and consultation data as described in the following sections.

Immunisation data

Uncoded consultation data are matched against immunisation data; if at least one match is found in the immunisation record, then these are marked as ‘scheduled’.

Therapy

Those that do not match with immunisation data are linked to medication data. If at least one match is found, they are marked as ‘unscheduled’.

Referral

Those that do not match with immunisation or therapy data are linked to referral data. If at least one match is found, they are marked as ‘unscheduled’.

Test

Those that are still uncoded are linked to test. If linked to test it is coded as either ‘scheduled’, ‘unknown’ or ‘unscheduled’ based on a review of the data. In general, if the test is part of the routine asthma review, then it is coded as ‘scheduled’; if it is testing peak expiratory flow rate then it is coded as ‘unknown’. Otherwise, it is coded as ‘unscheduled’ (full details are available on request).

When a consultation links to more than one record, the same rules of precedence apply as outlined in the Conflicting clinical contact types section.

Consultation data

For consultation data that are still ‘unknown’, ‘unlinked’ and, therefore, uncoded, consultation type is used to determine whether it is scheduled, unscheduled or not applicable (see Table 28 for a summary; full details are available on request). In this way, all contacts will now be coded as either ‘scheduled’, ‘unscheduled’ or ‘not applicable’.

TABLE 28

Consultation type coding

Emergency contacts

In addition to coding as scheduled, unscheduled and not applicable, some consultation types from the consultation table were coded as emergency (Table 29).

TABLE 29

Emergency contact codes