Each study register has its own user interface and system language with different features which makes it nearly impossible to find a “one-size -fits-all”-search- algorithm. The scientific scope of the search defines the search strategy for each register.
For instance, simple searches may be requested by certain agencies whereas searches aiming to identify evidence for systematic reviews may need to be more complex.
First, you need to think about the right search terms. Compared to bibliographic literature searches where one aims to achieve a balance between sensitivity and specificity of the search strategy, search strategies in study registers usually primarily aim for high sensitivity – deliberately accepting a potentially lower specificity.
Sensitivity is defined as the number of relevant reports identified divided by the total number of existing relevant reports. Specificity (i.e. precision) is defined as the number of relevant reports identified divided by the total number of reports identified.
Complex search strategies may not be the optimal solution to achieve high sensitivity. For instance, IQWiG recommends a rather simple search strategy with either the use of terms for the new therapeutic agent or the study indication. Only if there are too many hits, agent and indication should be combined.
When search terms need to be combined, one has to consider the different register-specific search features. While the common registers all utilize Boolean Operators (i.e. AND, OR, NOT) not all of them allow for hierarchic search algorithms using brackets (i.e. (A OR B) NOT C). Similarly truncation of search terms is not possible or advisable in all registers; truncation refers to replacing all theoretically possible word endings by an asterisk (e.g. immun* to find variations such as immune, immunity, immunoglobulins etc.). Some examples are depicted in the table below.