Data collection i.e. the measurement and recording of data, is considered to be the most crucial stage of the data management process. Errors made at this stage can be the most difficult to detect and to correct compared to those made at a later stage. Data management procedures at later stages can do little to improve the reliability and validity of the source data.
The first stage in designing the data collection strategy for a trial is to decide what data will be collected and at what time points (see Outcome Assessment). These decisions should be driven by the scientific objectives of the research and care should be taken to only collect data that are needed to meet the objectives. Investigators should keep the amount of data collected per participant to a minimum by referring to dummy tables (see Dummy tables).
Once it has been decided which data to collect, the investigator must choose how to collect the data. This may be by questionnaire, face-to-face interview, case note review, focus group, electronic record systems or through routinely collected data. Investigators should be aware of Data Protection legislation in their own country.
Illustrative example - Perinatal care trial
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Figure 2 presents a summary of all the staff that will be involved in data collection. All hospitals will receive one computer that will be used only for data management and operated by the data manager. Intervention hospitals will receive a second computer, but this equipment will be used by birth attendants and will have no role in data collection for primary and secondary outcomes. It will be used, however, to gather data on certain process measure, only in intervention hospitals.
Figure 2 Staff involved in data collection. The data collection system will be centrally coordinated at
CLAP by a statistician. The team at CLAP will include one programmer,
one statistical assistant, and two data clerks. The computer programmer
at CLAP will develop the software for data collection and validation.
The statistical assistant will carry out day-to-day data management
activities (communication with
data supervisor and data clerks at the hospitals, production of
monitoring
and validation reports, etc). For paper forms sent to CLAP, the two
data
clerks will perform two independent data entries. Two data supervisors
in
Argentina and one data supervisor in Uruguay will implement and
supervise
the data collection at the country level during the whole study period.
Data
supervisors will visit hospitals usually on a weekly basis, although
the
frequency of visits may vary according to hospital performance and
needs.
One data manager will be hired in each hospital. In most cases, this
personnel
will be one hospital employee that will work part-time for the project.
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Illustrative example - WHO pre-eclampsia
trial
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At each visit and at delivery, clinical data will be collected and recorded in forms designed for the study. Blood pressure Blood pressure measurements will be standardized. The equipment must be serviced locally before the initiation of the study. The subject should be at rest, seated, for 5 minutes; the cuff should be placed on the right arm at the level of the heart before the measurements. Two blood pressure measurements of systolic and diastolic will be taken using a standard sphygmomanometer at 3-minute intervals. Leave the cuff deflated on the subject's arm and wait for 3 minutes to take the second measurement. Diastolic blood pressure will be measured at the 5th Korotkoff sound, which is the disappearance of the sounds. At every centre, the trial coordinator will train staff on their abilities to measure blood pressure according to guidelines contained in the trial document: A practical guide on how to measure blood pressure and test for proteinuria. The trial coordinator will be trained before the initiation of recruitment. Retraining sessions will be carried out every three months. At monthly intervals, staff will be tested for reliability of blood pressure measurements. Test-retest procedures will be performed using a double stethoscope and results of the measurements will be recorded on appropriate forms to calculate agreement between examiners. Completed data collection forms will be returned to WHO in Geneva monthly; data checking and entry will be continuous. All data will be double entered, cleaned and queries checked immediately with the local investigators. Prompt return of data collection forms and speedy clarification of queries will facilitate verification of data. (WHO Multicentre Randomized Trial of Calcium Supplementation for the Prevention of Pre-eclampsia - go to protocol) |
This checklist has been contributed by Barbara Farrell who prepared
it for the second version of the Trial Management Guide.
This guide has been contributed by Barbara Farrell who prepared it for the second version of the Trial Management Guide.
These are a selection of schedules for data collection.
This checklist was a modified version of one developed by Barbara Farrell who prepared it for the second version of the Trial Managers Guide.
This site provides guidance for constructing, formatting and piloting a questionnaire.