Planning a Search: Search Terms and Strategies

Planning a Search

The focus of this section will be on the performance of a literature search on bibliographic databases. However, some of the general principles, and also the list of search terms relating to the Three Rs may also be applicable to searches carried out on an Internet search engine.

A literature search should always be an essential first step in the planning of any research. It is required in order to obtain an in-depth view of the field of the proposed study, to identify where knowledge is lacking, and to ensure that the planned research does not unknowingly duplicate work that has already been done. Avoiding the duplication of an animal study already contributes to a reduction in the use of animals.

Many people see the requirement to document their consideration of the Three Rs as a burden which increases the stress of the investigator at the last stage of project submission. Bringing the Three Rs principles into the first literature searches will not only avoid that later burden but may also result in a better, more efficient study.

For example, the use of in vitro models isolates the system under study from the rest of the organism, thus eliminating the confounding effects of systemic influences. This may provide a clearer picture of the mechanisms involved and may also give some information about the validity of the hypothesis underlying the planned research.

Even if subsequent in vivo work is required, the in vitro results may assist in identifying the parameters that need to be considered. Appropriate experimental design and appropriate analysis of the resulting data, with due consideration to statistical principles, can increase the precision of the data obtained and may also enable fewer animals to be used. The experience of pain and other stress is likely to result in physiological changes which may increase the variability of experimental results. Therefore, any refinements which increase the wellbeing of the animals and decrease pain and stress will help to improve the quality of the results. For all these reasons, it is useful to have an insight into how the 3Rs may apply to the proposed research right from the very start.

Initially, it is necessary to define search terms specific to the field of study and the research topic. The way in which these can be identified is described below. Once these terms have been identified, they will need to be combined into a search profile using Boolean or other operators. The use of operators is covered in the Search Basics section.

The use of parentheses and operators makes it possible to construct very long and complicated profiles which include the whole of the desired search. However, on systems which permit the storage and subsequent recall of individual search sets, it is better to do the search in a number of steps, each dealing with one concept, and then to combine the retrieved sets in various ways. This makes it easier to go back and adapt the various strategies if necessary since it is possible to see how many documents are being retrieved by each part of the search strategy. It is also useful to make brief notes on which combinations of which sets are being used at each stage. If the search ends up including many steps. it is sometimes quite difficult to remember exactly what was done in some of the earlier steps and to identify which sets to use again in order to refine the search.

If the first search retrieves too many documents, of which many are irrelevant, it will be necessary to make the search profile more precise. This may be done by using narrower terms, for example searching on "rats" instead of "rodents". Another trick is to limit the search on the most important terms to the title field, if that is permitted.

On the other hand, the first attempt may retrieve very few documents. In this case, some of the very specific parts of the search profile should be removed and/or broader search terms should be used. It may be possible to explode a search. This is possible on databases such as Embase and Medline which use a hierarchical indexing system. The policy of these databases is to assign the narrowest indexing term possible. For example, the Emtree system used by Embase has the index term "cell culture" and under this a number of terms describing specific types of cell culture.

A paper describing monolayer cultures will be indexed with the term "monolayer culture", while a paper describing cell cultures which are not listed among the more specific terms will be indexed with "cell culture". Therefore, searching on "cell culture" will not retrieve the documents on monolayer cultures if the search is limited to the descriptor field or, in the case of an all fields search, if the word cell does not appear in the abstract or title. Exploding the search term "cell culture" will retrieve all documents indexed with the terms listed below cell culture in the hierarchy. Therefore it will retrieve documents about monolayer cultures, but also those about fibroblast cultures, lymphocyte cultures, etc. Explosion may sometimes be useful, but it does entail the risk that a huge number of documents will be retrieved.

Having performed the subject-specific search, most scientists will want to obtain full copies of documents that appear relevant and go through these to see if the hypothesis is valid and if the proposed study is justified. This is a good opportunity to make notes of anything that might be relevant to the 3Rs. Are there any references to in vitro studies? Has any work been done on less evolved species? Has a particular strain of animal been shown to be more sensitive to the effects that will be studied? If yes, it may be possible to obtain statistically meaningful results using fewer animals than if a less sensitive strain was used. Any anaesthetics and analgesics used in the studies should be noted. It may be advisable to perform a further search on the effects of these compounds, because some may cause physiological changes which will have a confounding effect on the results, while others may result in fewer adverse effects. Are there any statistical models that have been developed for use in this type of study and will these affect the design of the experiments? Is there any mention of possible refinements such as the use of less invasive procedures, different methods of handling the animals or attempts to provide environmental enrichment?

Once this first analysis has been completed, a second search should be carried out to investigate further the possibility of replacement, reduction and refinement. The 3Rs cover a very broad set of concepts. A number of words relating to alternatives in general and to refinement, reduction and replacement are listed below. Appropriate words from these lists should be combined into search profiles together with some of the subject keywords.

As before, it is necessary to consider using synonyms, acronyms, spelling variants and truncation. At this stage, it may be a useful exercise to limit each search profile to subject-specific keywords expressing only one concept and maybe also to use some broader terms so as to extend the search into other disciplines. For the same reason, it may also be useful to try a search in a different set of databases.

At all stages, retrieval of relevant documents will be influenced by the different indexing policies and indexing systems of the different databases and the extent to which the search is tailored towards different indexing systems. Major database hosts such as Dialog permit a simultaneous search to be carried out across multiple databases. This can save a lot of time, but it does mean that it is not possible to optimise the search strategy to the indexing system of each individual database. It is worth trying to do this in subsequent searches on selected individual databases if a simultaneous search does not produce many relevant results. Libraries will sometimes have hard copies of database thesauri, and sometimes it is possible to view them on-line. If neither of these is available, retrieving the full records of known relevant articles from the selected database will show the indexing terms that are used by that database.

Subject-specific terms

The best way in which to generate a list of subject-specific terms is to identify a set of core papers about the subject. A good place to start is by looking through some review journals.

Once one or two pertinent reviews have been found, these can be used to identify important papers and important authors in the field. This may result in some older references being listed. It can be useful to follow these forwards in time by using the Web of knowledge index, to identify articles which have cited these key papers and key authors. Relevant words can then be extracted from the full texts of the core papers, including any keywords supplied by the authors.

The types of search terms that need to be considered relate to the following categories:

• the field of interest: e.g cardiology, pharmacology, neurology;

• the species used in the reported studies;

• the systems or anatomical structures that are studied;

• any pathological or physiological processes that might be involved;

• and any hormones, enzymes or chemicals of interest or relevance to the study.

Try to include synonyms, for example, heart can be used in place of cardiac. Also include any commonly-used acronyms, for example, GPT, NSAID. It is also important to think of possible variants in spelling as in the British and US spellings of tumour or foetus.

It may also be useful at this stage to go into one or two databases and retrieve the full records for some of these core papers. This can easily be done by searching on appropriate words from the title and author names in the title and author fields, and/or searching by date in the year field. The full records will show the words which have been used to index the articles for the databases. They may help to identify some more keywords. If many of the core papers cannot be retrieved from a database, this will serve as an alert that this database is not going to be very useful for the planned search.

If the indexing thesaurus should ideally be consulted, in order to obtain the preferred terms or indexing codes and also narrower and/or broader terms/codes for these concepts. Otherwise, attention once again has to be given to broader and narrower descriptions, possible synonyms, use of both singular and plural, likely usefulness of truncation and possible variations in spelling, as discussed in the Search Basics section.

General Search Terms: Examples

General Terms

alternatives or animal testing alternatives combined with:

• assay

• method

• model

• replace

• replacement

• surrogate

• system

• technique

Refinement

animal combined with:

• cage

• caging

• housing

• husbandry

• welfare

enrichment possibly combined with:

• behavioural

• environmental

• euthanasia

• handling

• restraint

• distress

• (non-)invasive

• pain

• postoperative

• postsurgery

• stress

• anaesthesia
  

• anaesthetic

• analgesia

• analgesic

• anxiolytic

• hypnotic

• sedative

Reduction

• reduce

• reduction

• experimental design

statistical combined with:

• analysis

• model

   

Replacement

Computers etc.

• artificial intelligence

• computer possibly combined with:

• aided/assisted instruction/learning

• image

• imaging

• interactive

• model (modelling)

• prediction

• simulation

• teaching

• expert system

• mathematical model (modelling)

• QSAR

• SAR

• structure-activity relationship

• software

• theoretical model (modelling)

• virtual

Physicochemical systems

physicochemical possibly combined with:

• artificial

• chemical

• physical

• assay

• membrane

• method

• model

• system

• technique

Non-mammalian organisms

• algae

• bacteria

• fish

• fungus

• hydra

• insect

• invertebrate

• microorganism

• plant

• protozoan

• yeast

• In vitro systems

appropriate combinations of the following:

• abattoir

• assay

• autopsy

• biopsy

• cadaver

• cell

• cell line

• cellular

• culture

• cytosolic fraction

• dermal equivalent

• embryo

• explant

• ex-vivo

• fragment

• human

• isolated

• method

• microsomal

• model

• organ

• organelle

• post-surgery

• slice

• subcellular fraction

• technique

• tissue

• tissue equivalent

• vitro ("in" is often a stop word which will be stripped from the search)