NHS Dental Services. Guide to Longitudinal Dental Treatment Files

Transcription

1 UK Data Archive Study Number Longitudinal Dental Treatment, NHS Dental Services

2 1. Table of Contents 1. Table of Contents 2. Purpose and scope 3. The GDS System 4. Definition of Dataset 5. Files and formats 6. Data Quality 7. Data Protection 8. Uses of the Dataset

3 2. Purpose and scope This guide is intended for prospective users of a set of files providing longitudinal data about the characteristics of, and dental treatments received by, a large sample of patients treated under the auspices of the NHS General Dental Services in England and Wales between 1990 and It describes the way in which the set of data was generated, provides metadata to explain the meaning of the variables, and gives examples of how the data may be used. In particular it makes reference to a supplementary Excel file containing the translations for the codes used in the file. It also explains the measures taken to ensure confidentiality of personal identities and caveats about the limitations of the data.

4 3. The GDS System To understand the data files it is useful to understand first the way in which the General Dental Services (GDS) payment system, from which the longitudinal data has been drawn, works. Throughout the period to which this dataset relates, dentists were paid by what is known as an Item of Service system. Every time a dentist reported that he had provided a specific treatment item for a particular patient a fee was generated for payment to the dentist. Dentists reported on treatment provided within a course of treatment at the end of that course of treatment. To do so the dentist would submit a claim in respect of the course of treatment. A course of treatment consisted of all the care and treatment which the dentist considered necessary to secure and maintain oral health, and which the patient was prepared to undergo. In effect, the course of treatment is a period of dental care terminating when the dentist considers the patient to be dentally fit. The primary record for dental care is thus the claim in respect of a single course of treatment. The claim record contains details about the dentist, the patient, the surgery, the start and end of the course of treatment, and the fees paid in respect of the claim, separately identifying patient charges collected by the dentist. In one course of treatment there may be one or more treatment items provided. These are recorded in treatment records attached to each claim record. The detail can vary from presence or absence (eg examination) or a count of items provided (eg radiographs) to a tooth level report on which teeth received the treatment (eg fillings). Throughout the period covered by the longitudinal data the process for paying dentists involved a monthly processing cycle whereby all the claims accumulated since the previous month were priced, using the treatment records, and drawn up into a schedule before generating a payment total for each dentist. Although there is a natural incentive on dentists to submit their claims as early as possible, there is an inevitable delay between the start of a course of treatment and its subsequent appearance on a dentist s payment schedule. Further delays may occur if subsequent corrections are submitted by the dentist. The consequence of this is that the historically published reports, which are based on the time of scheduling rather than start or completion of courses of treatment, are systematically time-shifted by comparison with this dataset, which takes into account all the corrections and late submissions received right through until processing of claims relating to courses of treatment starting before April 2006 ended in March 2007.

5 4. Definition of Dataset The sample is defined by the date of birth of the patient a set of twenty days in each calendar year was chosen on a stratified pseudo-random basis, and all those patients whose dates of birth fell within the set were chosen for the sample. For this defined set of patients all the General Dental Services records of payment claims with a date of acceptance on or after 1 st October 1990 form the substance of this dataset. Each payment claim relates to a single course of treatment with a defined date of acceptance this generally records the day when the course of treatment started. The data files contain records at, in effect, three levels: 1. Claim 2. Treatment 3. Tooth The claim level relates to the course of treatment. Each claim is followed by zero, one or more treatment records. Some treatment records include tooth notations. The three record levels can be linked by a unique claim ID number. It should be noted that it is possible to have more than one tooth notation record for the same treatment item and the same course of treatment, generally reflecting treatment provided under guarantee. It is also possible to have the same tooth reported more than once in the same record, when more than one composite resin or glass ionomer filling is provided. On a few rare occasions, the number of such fillings is such that there may be two quadrant records for the same quadrant. So far as practicable, the records have been consolidated to remove resubmissions and corrections, so that each claim record relates to one and only one course of treatment, and there is no duplication of corresponding treatment and tooth level records. The claim level records hold further information about the principal dentist responsible for the course of treatment, as well as the postcode area for the surgery at which the course of treatment was provided. To help with assessment of the likelihood of duplication of patient or identity, a supplementary indicator has been provided to show the relative frequency of occurrence of the patient surname within the population of patient IDs. The codes were originally defined in the Statement of Dental remuneration (SDR) ( which uses broad ranges of codes, known as chapters, to cover different groups of activity and patient types. It is important to be aware that some activity may be recorded in more than one chapter. In particular, there are separate chapters on occasional treatment and incomplete treatment, many of the codes in which mirror those in the earlier main chapters. Occasional treatment generally relates to treatment on patients who were not, at the time, registered with dentist who provided the treatment.

6 5. Files and formats The longitudinal file data are contained in three linked tab-delimited ASCII files, which can be read with most statistical and database packages. The three files are as follows: GDS claims.dat contains a record for each claim GDS treats.dat contains a record for each treatment item on each claim, excluding those which are tooth-specific GDS patts.dat contains a record for each tooth-specific item on each claim, giving the tooth positions of each tooth treated The file Variable metadata.xls contains chapter and verse for the structure and variable definitions within each of these three files. Broadly though, the three files are linked by a key variable, the claim ID, which for any given claim has exactly one record in GDS claims and one or more in either GDS Treats or GDS patts. GDS claims contains relevant information about the dentist and the patient, at the time of the course of treatment to which the claim relates, plus the dates of start and end of the course of treatment, where the surgery was located, and how much the course of treatment cost in gross fees (inclusive of any contribution from the patient). GDS treats contains records of individual treatment items coded as in the Statement of Dental Remuneration (see online for more detail). Against each treatment item is recorded a count of the number of instances (eg number of radiographs, number of visits). GDS patts is restricted to those treatment items for which a tooth notation is required. For each treatment it records the teeth treated, using the characters #, %, and to designate the four quadrants Upper Right, Upper Left, Lower Right and Lower Left respectively, and the numbers 1-8 and ABCDE and S (for supernumerary). There is also a record of the number of quadrants in which teeth were treated. Within the forty-character variable for tooth notation, the first, 11 th, 21 st and 31 st are occupied by quadrant designators, each followed by the corresponding tooth numbers within the quadrant. Analysing the GDS patts file requires the use of string functions to generate records of individual teeth. However, the format used retains the lowest possible level of detail, as well as a predictable file size. All the above files are net of normal corrections and deletions. This has been achieved by matching successive GDS treats records to remove pairs of claims, using all the available data from 1990 to This and associated cleaning exercises are described in the next section, on data quality.

7 6. Data Quality The data in these files is taken from operational systems, and although all known errors were corrected, it is clear, from the pattern of distribution of some variables, that some values are incorrect. What is more, the pattern of errors is not uniform, with a high concentration, understandably, soon after the start of the GDS contract in October Where appropriate, attention has been drawn to evident distortions in the Variable metadata.xls file. Dates of attendance and birth are particularly prone to error, especially at or around the year Since an important use of this data set is likely to be for longitudinal matching of patient identities, a specific variable has been created to help determine the impact of mis-matching. Two types of error may occur: matching two records which actually relate to two different patients, and having two patient IDs referring to the same patient. Most of this mismatching is thought to relate to the patient surname, so a measure of the frequency of the patient surname among the patient IDs in the database has been provided. The higher the frequency of the surname the more likely the former error. The rarer the surname the more likely that it has been mistranscribed, and hence the more likely that the second type of error has occurred. Users may find that using the surname frequency indicator for stratification allows them to test the sensitivity of their analyses to this type of error. Apart from the issue of accuracy of data recording, a cautionary note must also be sounded on the consistency of codes over time. Some codes were in use for only part of the observation period, and some changed the level of detail recorded between different years. There are also multiple codes, in some cases, for the same treatment, so great care is needed when developing time series analyses. Large year-on year changes in other treatment are a symptom of such changes to the codes. Some insight into the changes year by year can be gleaned from a study of the successive Digests of Statistics ( or the Statement of Dental Remuneration (SDR) ( There are also some internal codes, which are not documented in the SDR, although the equivalent SDR label is generally provided. Again, these internal codes may have been in use only for a limited period of time, and they are therefore more use as additional background information rather than primary data for time series analysis.

8 7. Data Protection There are two types of personal data in the source files used for this data set: that which identifies the patient, and that which identifies the dentist. Patient identity is hidden not only by the use of anonymised ID numbers, but also by the sample structure. There is only a small chance that a particular individual has associated records in the data set, and the details provided of age and location are too broad to be used to identify individuals, even in combination. All principal dentists under whose name any of the sampled patients received treatment are included in the dataset, but the identifying details of the dentists are limited to gender and year of birth. In some cases, the work itself will have been carried out by assistants or vocational dental practitioners, under the direction of the principal dentist, but details of this have not been retained in the records since this could help to identify individual dentists (because assistants and vocational dental practitioners represented only a very small part of the dental workforce).

9 8. Uses of the Dataset This dataset provides opportunities for both cross-sectional and longitudinal analysis. In particular, there is great scope for exploring the patterns of re-intervention on the same tooth, using techniques such as Kaplan-Meier and Cox-regression. Patients may be classified according to their long-term treatment and attendance patterns and then compared in terms of re-intervention rates. Some work in this area, conducted using a small subsample of this dataset, can be found in Lucarotti et al (2005) (Lucarotti PSK, Holder RL, Burke FJT. Analysis of an administrative database of half a million restorations over 11years. J.Dent.2005:33: ). However, it is not necessary even to use the full complexity of the data set in order to get useful analyses. The data can be aggregated by a wide range of variables to show geographical and temporal variation in rates of treatment intensity and patient and treatment volumes. Because of the data structure, these analyses can be carried out at different levels of precision, and standard errors can be determined by using bootstrap techniques. Furthermore, with appropriate caveats, the dataset may be used to confirm and then drill down into aggregate historical data which has already been published, such as the Annual Digest of Statistics published by the former Dental Practice Board ( By using randomised reference numbers for both dentists and patients, the dataset has been designed to facilitate the use of subsamples. It is easy, for example, to look at the experience of a sample of a thousand patients, simply by using the patient IDs below 1,001, or from 1,001 to 2,000 for example. The work of a hundred randomly selected dentists can be extracted by similar means. This may be particularly helpful for exploratory data analysis, hypothesis generation, and teaching purposes.