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A guide for finding quality information on food science and nutrition.

Formulating a research question


Tutorial| How to build an evidence based research question.

"PICO" is a mnemonic acronym to help you remember the elements that should be identified when formulating a question and search strategy to retrieve the most recent, pertinent, and valid research studies to guide decision making that results in quality healthcare.

P = Population (usually identifies a specific population with topic of interest)

I = Intervention

C = Comparison

O = Outcome

ADA Evidence-Based Practice

American Dietetic Association

ADA Evidence Analysis Library:

HIV/AIDS Guideline (December 2010)



Chronic Kidney Disease (July 2010)                               Hypertension (April 2008)
Unintended Weight Loss (Oct 2009)                                        Diabetes Type 1 & 2 (March 2008)  
Spinal Cord Injury (June 2009) Oncology  (Oct 2007)

 Celiac Disease (May 2009)

Pediatric Weight Management (June 2007)
Gestational Diabetes (Dec 2008)  Critical Illness  (Sept 2006)

COPD (Oct 2008)  

Adult Weight Management  (May 2006)
Heart Failure   (July 2008)  Disorders of Lipid Metabolism (2005)--Added DLM Triglyceride Recommendations

Research Methodologies in PubMed

PubMed MESH for research methodologies 

Paste the   term [mh]  OR  term [pt]   into PubMed search box


Prospective Studies [mh]    

Observation of a population for a sufficient number of persons over a sufficient number of years to generate incidence or mortality rates subsequent to the selection of the study group.


Retrospective Studies [mh] 

Studies used to test etiologic hypotheses in which inferences about an exposure to putative causal factors are derived from data relating to characteristics of persons under study or to events or experiences in their past. The essential feature is that some of the persons under study have the disease or outcome of interest and their characteristics are compared with those of unaffected persons. 

Cross-Sectional Studies  [mh]  

Studies in which the presence or absence of disease or other health-related variables are determined in each member of the study population or in a representative sample at one particular time. This contrasts with LONGITUDINAL STUDIES which are followed over a period of time. 

Longitudinal Studies [mh]

Studies in which variables relating to an individual or group of individuals are assessed over a period of time.

Qualitative Research [mh]

Research that derives data from observation, interviews, or verbal interactions and focuses on the meanings and interpretations of the participants.


Quantitative Studies

a   Case Reports [mh]

Clinical presentations that may be followed by evaluative studies that eventually lead to a diagnosis.

aa Case Control Studies [mh]

Studies which start with the identification of persons with a disease of interest and a control (comparison, referent) group without the disease. The relationship of an attribute to the disease is examined by comparing diseased and non-diseased persons with regard to the frequency or levels of the attribute in each group.

b  Cohort Studies [mh]

Studies in which subsets of a defined population are identified. These groups may or may not be exposed to factors hypothesized to influence the probability of the occurrence of a particular disease or other outcome. Cohorts are defined populations which, as a whole, are followed in an attempt to determine distinguishing subgroup characteristics.

c   Clinical Trials [pt]

Work that is the report of a pre-planned clinical study of the safety, efficacy, or optimum dosage schedule of one or more diagnostic, therapeutic, or prophylactic drugs, devices, or techniques in humans selected according to predetermined criteria of eligibility and observed for predefined evidence of favorable and unfavorable effects. While most clinical trials concern humans, this publication type may be used for clinical veterinary articles meeting the requisites for humans. (PubMed LIMIT)

cc Randomized Controlled Trials [pt]          

Work consisting of a clinical trial that involves at least one test treatment and one control treatment, concurrent enrollment and follow-up of the test- and control-treated groups, and in which the treatments to be administered are selected by a random process, such as the use of a random-numbers table.  (PubMed LIMIT)

ccc Controlled Clinical Trials [pt]

Work consisting of a clinical trial involving one or more test treatments, at least one control treatment, specified outcome measures for evaluating the studied intervention, and a bias-free method for assigning patients to the test treatment. The treatment may be drugs, devices, or procedures studied for diagnostic, therapeutic, or prophylactic effectiveness. Control measures include placebos, active medicine, no-treatment, dosage forms and regimens, historical comparisons, etc. When randomization using mathematical techniques, such as the use of a random numbers table, is employed to assign patients to test or control treatments, the trial is characterized as a RANDOMIZED CONTROLLED TRIAL   (PubMed LIMIT)

d  Epidemiological Studies [mh]

Studies designed to examine associations, commonly, hypothesized causal relations. They are usually concerned with identifying or measuring the effects of risk factors or exposures. The common types of analytic study are CASE-CONTROL STUDIES, COHORT STUDIES, and CROSS-SECTIONAL STUDIES.

e  Meta-analysis [pt]

Works consisting of studies using a quantitative method of combining the results of independent studies (usually drawn from the published literature) and synthesizing summaries and conclusions which may be used to evaluate therapeutic effectiveness, plan new studies, etc. It is often an overview of clinical trials. It is usually called a meta-analysis by the author or sponsoring body and should be differentiated from reviews of literature.  (PubMed LIMIT)


Additional PubMed MESH for studies

Multi-center Study [pt]


Controlled studies which are planned and carried out by several cooperating institutions to assess certain variables and outcomes in specific patient populations. For example, a multi-center study of congenital anomalies in children. (PubMed LIMIT)


Evaluation Study [pt] 


Studies determining the effectiveness or value of processes, personnel, and equipment, or the material on conducting such studies. For drugs and devices, CLINICAL TRIALS, DRUG EVALUATION, and DRUG EVALUATION, PRE-CLINICAL are available. (PubMed LIMIT)


Validation Study [pt]


Works consisting of research using processes by which the reliability and relevance of a procedure for a specific purpose are established. (PubMed LIMIT)



Secondary Resources


Meta-analysis [pt]

Works consisting of studies using a quantitative method of combining the results of independent studies (usually drawn from the published literature) and synthesizing summaries and conclusions which may be used to evaluate therapeutic effectiveness, plan new studies, etc. It is often an overview of clinical trials. It is usually called a meta-analysis by the author or sponsoring body and should be differentiated from reviews of literature.  (PubMed LIMIT)


Systematic Reviews      (enter  search as follows)      systematic [sb]   





Cochrane Handbook  |  1.2.2  What is a systematic review?

A systematic review attempts to collate all empirical evidence that fits pre-specified eligibility criteria in order to answer a specific research question.  It  uses explicit, systematic methods that are selected with a view to minimizing bias, thus providing more reliable findings from which conclusions can be drawn and decisions made (Antman 1992, Oxman 1993). The key characteristics of a systematic review are:

  • a clearly stated set of objectives with pre-defined eligibility criteria for studies;

  • an explicit, reproducible methodology;

  • a systematic search that attempts to identify all studies that would meet the eligibility criteria;

  • an assessment of the validity of the findings of the included studies, such as through the assessment of risk of bias; and

  • a systematic presentation, and synthesis, of the characteristics and findings of the included studies.

Many systematic reviews contain meta-analyses. Meta-analysis is the use of statistical methods to summarize the results of independent studies (Glass 1976). By combining information from all relevant studies, meta-analyses can provide more precise estimates of the effects of health care than those derived from the individual studies included within a review (see Chapter 9, Section 9.1.3). They also facilitate investigations of the consistency of evidence across studies and the exploration of differences across studies.





Review [pt]


An article or book published after examination of published material on a subject. It may be comprehensive to various degrees and the time range of material scrutinized may be broad or narrow, but the reviews most often desired are reviews of the current literature. The textual material examined may be equally broad and can encompass, in medicine specifically, clinical material as well as experimental research or case reports. State-of-the-art reviews tend to address more current matters. A review of the literature must be differentiated from HISTORICAL ARTICLE on the same subject, but a review of historical literature is also within the scope of this publication type.







Surveys on dietary intake and nutritional studies

Search Using MESH

Search MeSH when retrieving long-standing and commonly used Nutrition concepts such as Nutrition Assessment, Nutrition Surveys, and Diet Surveys.  

Enter the first MESH term into the PubMed search box.  When you search Nutrition Assessment [mh], PubMed uses an "Explode" strategy to augment your search that also searches the narrower MESH terms found in the MESH hierarchy in the MESH Database. 

 Nutrition Assessment [mh]                                                  

         Nutrition Surveys [mh]  

                 Diet Surveys [mh]


Find definitions for MESH terms - Go to MESH Database

Nutrition Assessment  | Evaluation and measurement of nutritional variables in order to assess the level of nutrition or the NUTRITIONAL STATUS of the individual. NUTRITION SURVEYS may be used in making the assessment.

Nutrition Surveys  | A systematic collection of factual data pertaining to the nutritional status of a human population within a given geographic area. Data from these surveys are used in preparing NUTRITION ASSESSMENTS

Diet Surveys  |Systematic collections of factual data pertaining to the diet of a human population within a given geographic area.



Search acronymns (NHANES) using Keywords

Some concepts that you search will not yet have or ever have MESH controlled vocabulary assigned to them.  Terms without MESH include acronyms like NHANES. Search NHANES two ways. First, search for the acronym in the title by entering it as follows      nhanes [ti]   

nhanes [ti]

If you wish to broaden your search to see articles that include your terms in the abstract too, just perform a keyword search without limiting to a field.



Search several synonyms at once using keywords          

Without MESH to identify articles that truly cover your topic, searching a keyword in the title better distinguishs articles that truly cover your topic from those that do not. Without MESH to map all articles using other synonyms to your topic, repeat your search with each synonym.  You can search several synonyms together by using OR as illustrated below.

obese OR obesity OR overweight


What is the MESH term for obesity?     

A status with BODY WEIGHT that is grossly above the acceptable or desirable weight, usually due to accumulation of excess FATS in the body. The standards may vary with age, sex, genetic or cultural background. In the BODY MASS INDEX, a BMI greater than 30.0 kg/m2 is considered obese, and a BMI greater than 40.0 kg/m2 is considered morbidly obese (MORBID OBESITY).

All MeSH Categories

         Analytical, Diagnostic and Therapeutic Techniques and Equipment Category


                              Diagnostic Techniques and Procedures

                                          Physical Examination

                                                Body Constitution

                                                      Body Weights and Measures

                                                            Body Size

                                                               Body Weight



                                                                        Obesity, Morbid


Searching PubMED with Keywords and MESH

PubMed designed for novice and the expert

PubMED offers two search strategies: MESH (Medical Subject Heading) and KEYWORD.  Using these together quickly accesses the most relevant articles and provides you with control of your search. 

PubMed subject specialists assign MESH terms to articles that truly cover the topic and assign the same MESH term to articles even then an author uses a different synonym for the topic. Thus, it maps all articles to one MESH term that cover your topic.

If MESH existed for every term, KEYWORD searching  would not be required.  MESH is assigned to every article, but there is a time delay before newly entered articles are assigned MESH. Additionally, acronymns are not assigned MESH. New drug names, new terms and newly coined phrases take a while to be formally defined, widely used, and formally adopted by the professionals using it; only then is MESH assigned.  

First search for keywords in TITLE, then in ALL FIELDS, then search using MESH.  Search history and combine search sets, click HISTORY.  To see how PubMED searches your terms entered into the search box, click DETAILS.

Find MESH terms in three places 

There are three ways to identify MESH terms.  

Find MESH terms with their definitions in the MESH DATABASE.  Once you find a useful term send it to PubMed to be searched. To search MESH term: Check the box next to the term, at far left, click LINK, at opened menu select "PubMed" to send to be searched.  Click HISTORY to see search strategy so far.

Find MESH terms in DETAILS. after entering and searching a term; click the DETAILS tab to see how PubMed searched it. Copy and paste the MESH term into the search box.

When viewing articles retrieved from a search, switch Display from Summary view to CITATION view and scroll below abstract to view the MESH for each article that has been processed and assigned MESH.  If you see an useful  highlighted MESH term following the abstract, just clicking it will send it to PubMed to be searched.


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