A Database is not what you think and different designs serve different purposes.

Vienna, June 11th, 2005

Different designs of LOS

Different designs of longitudinal observational studies (databases, registries, cohort studies) serve different purposes Loreto Carmona

Research Unit Spanish Society of Rheumatology



Why this talk?

• Sometimes the only point in which investigators agree in a given project is about the need to collect data.

• There is indeed much misunderstanding about databases.

• The first principle of data collection: We should not collect data just for the sake of it, without explicit and specified objectives.



What is a database?

NOT:

Any set of data entered into a computer

YES:

A tool to organize the data in a study



What is not a database?

A dataset



Other uses



What is a database?

• Organizing

• Hierarchical

• Relational



Structure

patient

treatment

treatment

treatment

treatment

AE

AE

AE

AE

AE

AE



Structure

patient

visit

visit

visit

visit

outcome

outcome

outcome

outcome

outcome

outcome



Time and databases

Medicaldatabases

timeLongitudina

lObservation

alStudies



Can we analyse data directly from a DB?

wide long



wide



long



Types of databases

Depend on the purpose and design of the study they serve.



Types of databases

1. Registries

2. Cohorts

3. Administrative databases

4. Clinical databases



Registries

• The introduction of new elements is not pre-planned (no schedule).

– relate to the pace of patients entry

– events entry

• The purpose of the registry defines the types of registry:

– Disease registry

– Drug registry



Registries

• Disease registry:– to estimate incidence of diseases

– pace of new entries = occurrence of new cases

• Drug registry:– The main purpose of such registries is the

identification of adverse events

– pace of entry = initiation of new treatments, of a target drug or therapeutic group, in patients who meet the inclusion criteria



Cohorts

• Studies set up for testing hypotheses. – Sensu strictu aetiological hypotheses

– they can also be assembled to test prognosis, or to test resource use hypothesis

• Subjects in a cohort must be sampled in a probabilistic way (to be representative).

• Timing of data entry pre-established in visits or examinations at a given interval (periodical).



Cohorts (concepts)

• Inception cohort– all new cases

– or early

• Nested case-control studies– advantage: cases and controls selected equally



Cohorts (concepts)

• Open cohorts– Permanent incorporation

– allow the study of the simultaneous influence of calendar time, age (duration) and cohort (onset) in demography, epidemiology, and clinical follow-up



Cohorts (concepts)



Cohorts (concepts)

• Closed cohorts– specific research objective (sample size)

– recruitment period

– subjects become older with follow-up

• Permanent surveys– examination over time is established in

repeated cross-sectional surveys

large open cohorts which are monitored over such a long time (Framingham study)



Cohorts (concepts)

• Randomised controlled trials

– cohorts in which the hypothesis is the efficacy of an intervention

– Not a LOS (planned intervention)



Cohorts (concepts)

• Aren’t prognosis or resource use studies cohorts?

– OK if the sample is selected in a probabilistic way

– and the hypothesis is pre-established before the launch of the cohort:• link between exposure to prognostic factors

(i.e. determinants) and rate of occurrence of outcome

• link between determinants and rate of use or cost



Types of databases

1. Registries

2. Cohorts

3. Administrative databases

4. Clinical databases



Administrative databases

• Specific purpose: managing the economic and organization aspects

• They allow to assess and preview:– the need of workforce – allocation of resources– logistic needs– insurance monitoring– costs, etc.



Administrative databases as surrogatesPROS

• rapid response (availability)

• large sets of population (increases statistical power)

CONS

• severe selection bias



Administrative databases’ best use

• To cross-check data in clinical databases:

– to confirm death,

– work status,

– drug consumption...



Clinical databases

• Quite often physicians record patients characteristic and variables directly from their practice in an intent to monitor health care practices.

• The resulting clinical databases are useful to:– retrieve patients’ reports

– Retrieve individual clinical histories

– assess the individual practice composition of a department or a clinic



Clinical databases’ bias

• The patients included have not been selected in a probabilistic way, what precludes the use of formal hypothesis testing statistical instruments.

• Representativity

• Difficulty to record all variables with the expected quality of a main outcome variable if one does not know ahead of time what the main outcome variable will be (study protocol)



Clinical databases’ best use

• To monitor practice

• To identify patients with a given characteristic, and to use them to draw a random sample, better if multicentre, and to test prospectively a research hypothesis



Conclusions

• We should bear in mind the meaning and use of databases.

• Different types of databases serve very different purposes.

• A clear understanding of the different investigation designs should avoid many of the databases we launch be just a lot of work and very little of science.

A Database is not what you think and different designs serve different purposes.

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