PRISMA is 'useful when planning and conducting systematic reviews to ensure that all recommended information is captured'¹.

• PRISMA Preferred Reporting Items for Systematic Reviews and Meta-Analyses.
  The site includes a:
  
  • checklist for Cochrane type systematic reviews and meta-analyses.
  • Use the checklist in conjuction with the PRISMA 2020 explanation and elaboration 
  • PRISMA flow diagram generator for you to document your search results.
    
  • PRISMA extensions for eg diagnostic test accuracy, harms, network meta analyses.
  • There is also a PRISMA-S PRISMA Search Reporting extension and a PRISMA-P for a protocol.

Note also:

• The Equator site also has the PRISMA guideline and extensions including preclinical invivo animal experiments, living systematic reviews PRISMA-C reporting for children, plus many other reporting guidelines for study types eg PRIOR for overviews of reviews, ENTREQ, eMERGe, TRIPOD, MOOSE etc
• RAMSES II Reporting standards for realist evaluations. See also Ramses projects
• ROSES RepOrting standards for Systematic Evidence Syntheses in environmental research
• STORIES Statement: publication standards for healthcare education evidence synthesis

1. Page, M. J., McKenzie, J., Bossuyt, P., Boutron, I., Hoffmann, T., Mulrow, C., … Moher, D. (2020, September 14). The PRISMA 2020 statement: an updated guideline for reporting systematic reviews. https://doi.org/10.31222/osf.io/v7gm2 p.7

Use  a framework such as PICO to create or help clarify your review question. A framework can also help to identify words in your systematic review question to use in your searches and to start building your search strategy.

PICO can be useful for a quantitative review. Something in the P and in the I section is sufficient in most cases for planning your search strategy.

PEO (Population, Exposure, Outcome) or PICo (Problem/population, phenomenon of Interest, Context) might be useful for qualitative reviews. Further explanations, additional/alternative frameworks and examples are at Clarify.

There is a handy table of Review type, aim, question format ie mnemonics, and question examples in: Munn Z, Stern C, Aromataris E, Lockwood C, Jordan Z. What kind of systematic review should I conduct? A proposed typology and guidance for systematic reviewers in the medical and health sciences. BMC Medical Reserch Methodology. 2018;18(1):5.

The systematic review process consists of taking a structured question, breaking it down into an itemised search procedure and if necessary applying a methodological filter.¹

First steps

• Make a concept map to plan your search.
  To see what this is and how to create one look at the Flinders University Library pdf SR searching guide. They refer to the concept map as a logic grid.

• Look at the search strategies of other relevant systematic reviews or meta analyses.
  Find recent systematic reviews, preferably a Cochrane review, which have a concept or component in common with your search topic, and look at their search strategies. Search strategies will usually be in either an appendix or part of the methods section. Use/adapt relevant ones for your search.
  
  
• If you know an author who has done a non-Cochrane systematic review similar to your topic find the paper and look for the search strategy - this may be an appendix (usually under a supplementary material link on a webpage) or briefly written up in the Methods section.

• Check the indexing of relevant systematic reviews.
  Do an initial search in a database. Select a relevant result, look at the database record and note down relevant words from the article title, abstract, author keywords and any MeSH, Emtree or Subject Headings.

• Next start 'systematically' constructing your search in the databases beginning with one database (usually Medline (Ovid)), one concept at a time, using a combination of subject headings (if available in the database) and keywords combined logically.

Reminder: Because a systematic review aims to be comprehensive, finding as many relevant studies as possible, the searching can be: time consuming pedantic and rigorous - using a mix of subject headings and keywords that need to be translated and adapted across the databases favours sensitivity over specificity - it is not unusual, depending on your topic, to have a total of 3,000-20,000 results. Think again if you have over 20,000 results. The search process is iterative and it may take some time to finalise your search strategy. You will need to test, adjust and retest your searches. 'The key to a good systematic review search strategy is lots of testing' University of Melbourne Library. Systematic reviews, Resources and strategies, Keywords, synonmns and shortcuts. Have a look at Smart searching: Logical steps to building and testing your literature search.

1 Booth A, Carroll C. Systematic searching for theory to inform systematic reviews: is it feasible? Is it desirable? Health Information & Libraries Journal. 2015: doi:10.1111/hir.12108

Databases

Have a look at some Cochrane reviews or other systematic reviews similar to your topic to see what databases they have used. At a minimum these databases need to be searched:

• Cochrane CENTRAL [Central Register of Controlled Trials] - part of the Cochrane Library - if you are searching for rcts.
• Medline
• Embase

Consider also searching:

• Web of Science Core Collection part of the Web of Science. The Emerging Sources Citation component of Web of Science Core Collection has regional journals including for public health. WSCC is also useful particularly if you are looking at adverse effects/events

Depending on your topic you may need to search additional databases

• CINAHL Plus particularly for a qualitative review, nursing and allied health
• APA PsycINFO
• Scopus

And some of these more subject specific databases:

• AMED for complementary medicine
• Web of Science for the Russian Science Citation Index, the SciELO citation index and the KCI Korean Journal database
• FSTA: Food Science and Technology Abstracts
• China Academic Journals from CNKI (China National Knowledge Infrastructure)
• EconLit - for economic evaluations
• PEDro - Physiotherapy evidence database
• OTseeker - Occupational therapy evidence
• LILACS Latin America and the Caribbean health sciences literature
• Informit - a suite of of New Zealand and Australian databases from which single or multiple databases can be searched
• Global Index Medicus - with access to more specific regional databases and Lower and Middle Income countries (LMICs)
• ALOIS - From the Cochrane Dementia and Cognitive Improvement group 'controlled trials that have been completed, are ongoing or are planned in the areas of dementia (prevention and treatment), mild cognitive impairment and cognitive improvement...updated every month from searches of a wide range of databases and clinical trials registries, with the help of a team of volunteers'.
• Bibliomap - EPPI Centre database of health promotion research
• SPORTDiscus
• International Pharmaceutical Abstracts
• Contemporary Women's Issues
• CRD database Centre for Reviews and Dissemination, University of York - is also part of the Cochrane Library database but this version has explanation about coverage up to 2015 and has DARE, NHS EED (Economic Evaluation Database) and HTA databases. The HTA component is useful for grey literature.
• NOURISHING and MOVING databases
• 3IE for LMIC topics
• If your topic leans more towards chemical sciences consider looking at Springerlink
• If your topic is interdisciplinary eg social sciences or education have a look at Databases by Faculty or Subject
• The Information Specialists at the University of Leeds have a useful and extensive list of Resources for finding trials.
• If you are doing an overview or review of reviews Medline and Epistemonikos must be searched. Note Epistemonikos results are also on the Other tab on the results screen in the Cochrane Library. There is a list of databases Epistemonikos searches.

Start with one database (usually Medline (Ovid)) to create your search then adapt/translate it as appropriate to run across the other databases you choose to search.

What about Google Scholar?

Usually not because Google Scholar searches cannot be reliably replicated.  However Bramer et al recommend searching it and use the first 200 references in the relevance ranking.
Bramer WM, Rethlefsen ML, Kleijnen J, Franco OH. Optimal database combinations for literature searches in systematic reviews: a prospective exploratory study. Systematic reviews. 2017 Dec;6(1):245.

Important to document your databases correctly.

Ovid, Ebsco and Proquest are platforms that host a number of individual databases. When documenting your search use the specific name of the database you used. If you used Medline and Embase add the platform to the database name eg

• Medline Epub Ahead of Print, In Process & Other Non-Indexed Citations, Ovid MEDLINE (R) Daily, and Ovid MEDLINE (R) 1946-Present (Ovid)
• Embase (Ovid)

when documenting the databases you searched. Make sure you include what bits of Medline you have searched ie Medline Epub Ahead of Print, In Process & Other Non-Indexed Citations, Ovid MEDLINE (R) Daily, and Ovid MEDLINE (R) 1946-Present (Ovid).

Grey Literature

If you are doing an in-depth systematic review you will need to search the Grey literature. In particular search the WHO International Clinical Trials Registry Platform and clinicaltrials.gov. (See the Cochrane Handbook 4.3.3)
See also from the Cochrane Collaboration:

• Clinical trials registers and regulatory databases. Includes import filters for EndNote.
• Identifying trials including handsearching.

Use a structured approach to your searches. Here is an example of a structured search in Medline (Ovid)

Source: https://guides.library.utoronto.ca/c.php?g=577919&p=3987363

Review your final search

Because you will take a lot of time to construct your final database searches make sure you check for eg spelling mistakes, incorrect use of AND and OR when combining searches etc  before running the final search and selecting appropriate results.

Highly recommended
The following has search hints and notes common errors and pitfalls in search strategies. Use it to review or ask a peer to review your final search strategies:

McGowan J, Sampson M, Salzwedel DM, Cogo E, Foerster V, Lefebvre C. PRESS Peer Review of Electronic Search Strategies: 2015 Guideline Statement. J Clin Epidemiol. 2016;75:40-6.

The PRESS E&E (Explanation & Elaboration) guide is on the CADTH website.

• PRISMA Preferred Reporting Items for Systematic Reviews and Meta-Analyses.
  • Use the checklist in conjuction with the elaboration and explanation documents.
  • PRISMA flow diagram generator for you to document your search results
  • There is also a PRISMA-S PRISMA Search Reporting extension.
    
    
• Consider using xls templates to document your search strategies, search dates, results and duplicates numbers. University of Texas - click the Tracking Results tab; Cochrane EPOC Search audit template

• SuRe Info has a brief overview of Documenting and reporting the search process. Included is a useful Elements of the Search to be Reported Table 1.pdf 212.79 KB

• See also: 4.5 Documenting and reporting the search process in the Cochrane handbook.

• The University of York Centre for Reviews and Dissemination guidebook on systematic reviews has useful wording on following up references and citations (p.251)

• Cochrane Information Specialists have a template text for search methods.

Most published systematic reviews are now required to include the database searches.
These are usually in the Appendices of the review. it is important to specifiy which platform or search interface hosted the databases you searched eg Medline (Ovid).

Generally the searches in each database are listed one after the other, or the Medline search is documented with a proviso ie 'The MEDLINE strategy and RCT filter are adapted to identify trials in other electronic databases'.

Chong J, Leung B, Poole P. Phosphodiesterase 4 inhibitors for chronic obstructive pulmonary disease. Cochrane Database Syst Rev. 2013(11):CD002309.

An alternative method to record searches is:

Pinnock H, Epiphaniou E, Pearce G, Parke H, Greenhalgh T, Sheikh A, et al. Implementing supported self-management for asthma: a systematic review and suggested hierarchy of evidence of implementation studies. BMC Med. 2015;13(1):1-18.

If you are updating a search see:

• Cochrane advice on updating searches.
• how to instructions from McGill University Library.
• How to from the University of Texan MD Anderson Center Library