Difference between revisions of "Opasnet Base (2008-2011)"

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This page is a general description about Opasnet Base. For a detailed description of its structure, see Opasnet Base structure. <section begin=glossary />

Opasnet base is a part of Opasnet and a storage and retrieval system for results of variable and data from studies. It is designed to be flexible enough to store information in almost any format: probability distributions or deterministic point estimates; spatially or temporally distributed data; or data with multiple dimensions. It can be used as a direct source of model input data, thus making it possible to use shared input information sources such as population data, climate scenarios, or dose-responses of pollutants. Opasnet Base can be accessed via links on variable and study pages (e.g. the metadata box), via a web interface and via the model Opasnet base connection.ANA.

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Some uses of Opasnet Base

Storage of interpreted model results

Originally, Opasnet base was designed to be the storage for interpreted model results, i.e. variable results. Variables attempt to answer specific real-world questions, and their results are the current best attempts to answer these questions. This is different than with studies that report the observations from a single study. Variable results are expected to improve in time eternally, while data from a study is fixed after the study has been done and observations made.

Storage of study results

Opasnet Base can be used to collect observation data from studies. A study can be a traditional research study, which is documented in Opasnet Data afterwards, or it can be an Opasnet study where the data is collected on a particular page of Opasnet using a web form. There are several purposes:

• To collect observation data to be directly usable in interpretations of variables and other objects.
• To collectively collect information about specific cases, and based on these data conditionalise a generalised assessment model with data specific to a particular case.

However, there are some things about variables and studies that should be understood:

• The object for a collection of observations is called a study, while the object of interpretations is called a variable. As an example, a study can collect information about a population group by a questionnaire and by taking a blood sample. The study identifier is the Obj.id in the Opasnet Base.
• The object may be divided into smaller pieces along one or more indices. For example, the questionnaire may have 30 questions, and therefore the questionnaire data can be indexed by an index with 30 columns (or rows, depending on which way you think), one row for each question. Each column of the study object has one cell, i.e. an answer to one question. In this study, ten blood markers will be studied, and therefore the study object will have 40 cells, and the index has 40 columns (30 from the questionnaire, 10 from the blood sample). The cell identifier is the Cell.id in the Opasnet Base.
• For each individual patient, there is one row of observations, each 40 cells. The observation row identifier is Res.Sample in Opasnet Base.
• The actual result of a particular cell of a particular patient is located in Sam.Result in Opasnet Base (or in Res_info.Description in the case where the result is text, i.e. non-numeric).
• Each study may be multidimensional just like a variable and have indices along e.g. space, time, or sex.
• If the data is collected using an Opasnet web form, then the timestamp and username or IP will be recorded for each entry into Resinfo.When and Resinfo.Who fields, respectively. This is not needed, if the data comes from a previously performed study (which is static data in the eyes of Opasnet).
• In some cases, it might be useful to restrict the number of entries per user to one. However, this is done only at the interpretation phase where only the last entry is counted. There are no restrictions to enter new data, and therefore a user may change his/her previous entry by simply making a new entry.

Making value-of-information analyses in Opasnet base

Value of information (VOI) is a decision analysis tool for estimating the importance of remaining uncertainty for decision-making. Result database can be used to perform a large number of VOI analyses, because all variables are in the right format for that: as random samples from uncertain variables. The analysis is done by optimising an indicator variable by adjusting a decision variable so that the variable under analysis is conditionalised to different values. All this can in theory be done in the result database by just listing the indicator, the decision variable, and the variable of interest. Practical tools should be developed for this. After that, systematic VOI analyses can be made over a wide range of environmental health issues.

Analysing the change in the quality of a variable result in Opasnet base

All results that have once been stored in the result database remain there. Old results can be very interesting for some purposes:

• The time trend of informativeness and calibration (see performance) can be evaluated for a single variable against the newest information.
• Critical pieces of information that had a major impact on the informativeness and calibration can be identified afterwards.
• Large number of variables can be assessed and e.g. following questions can be asked:
  • How much work is needed to make a variable with reasonable performance for practical applications?
  • What are the critical steps after which the variable performance is saturated, i.e., does not improve much despite additional effort?

See also

• Opasnet Base structure
• Opasnet
• Open assessment
• Opasnet base connection.ANA