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Intervention Protocol

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Water-based exercise for asthma in adults

  1. Antonio Jose Grande1,*,
  2. Valter Silva1,
  3. Brenda NG Silva1,
  4. Rachel Riera1,
  5. Sergio A Parra2,
  6. Maria S Peccin3

Editorial Group: Cochrane Airways Group

Published Online: 30 APR 2013

DOI: 10.1002/14651858.CD010456

How to Cite

Grande AJ, Silva V, Silva BNG, Riera R, Parra SA, Peccin MS. Water-based exercise for asthma in adults (Protocol). Cochrane Database of Systematic Reviews 2013, Issue 4. Art. No.: CD010456. DOI: 10.1002/14651858.CD010456.

Author Information

  1. 1

    Centro de Estudos de Medicina Baseada em Evidências e Avaliação Tecnológica em Saúde, Brazilian Cochrane Centre, São Paulo, São Paulo, Brazil

  2. 2

    Universidade Estadual de Londrina, Londrina, Parana, Brazil

  3. 3

    Universidade Federal de São Paulo, Department of Human Movement Sciences, Santos, São Paulo, Brazil

*Antonio Jose Grande, Brazilian Cochrane Centre, Centro de Estudos de Medicina Baseada em Evidências e Avaliação Tecnológica em Saúde, R. Borges Lagoa, 564 cj 63, São Paulo, São Paulo, 04038000, Brazil.

Publication History

  1. Publication Status: New
  2. Published Online: 30 APR 2013


This is not the most recent version of the article. View current version (17 JUL 2014)



  1. Top of page
  2. Background
  3. Objectives
  4. Methods
  5. Acknowledgements
  6. Appendices
  7. Contributions of authors
  8. Declarations of interest
  9. Sources of support

Description of the condition

Asthma is a disease characterised by inflammation of the airways which causes airflow obstruction (CDC 2011; Lucas 2005; WHO 2011). Although frequency and intensity vary from person to person, the symptoms of asthma are breathlessness, wheezing, coughing, chest tightness and pain (Banzett 1985; CDC 2011; WHO 2011). Epidemiological data from a survey applied in 70 countries estimate that 623 million individuals worldwide are currently living with some level of asthma-related symptoms (To 2012); asthma is ranked as one of the most prevalent conditions globally. It is also important to consider the economic impact of this disease; the United States spends around 30 billion dollars per year on emergency department visits, physician visits and medication (CDC 2011). The Center for Disease Control and Prevention (CDC) estimated in 2006 that there were 1.6 million emergency department visits and 440,000 hospitalisations in the USA (CDC 2011).


Description of the intervention

It may be inferred that some people with asthma are limited in what physical activities they can undertake and that this may result in a sedentary lifestyle. Indeed, people with asthma are more likely to suffer from cardiovascular and metabolic conditions (Corbin 2011; Goodman 2008; Hildenbrand 2010). Undertaking physical activity is important to improve quality of life in people with asthma (Lucas 2005; Pedersen 2006). Water-based exercises are a good treatment option and these exercises increase muscular strength, cardiorespiratory fitness and flexibility, and improve body composition (reducing body fat and increasing muscle mass) (Ambrosini 2010; Avelar 1999; Corbin 2011; Malkia 1998). Furthermore, muscle strength and cardiorespiratory fitness have a positive association with a reduction in the incidence of acute exacerbations (Gonçalves 2008). The most common water-based exercises described in the literature are swimming, hydrogymnastics and hydrotherapy (Denning 2012; Hildenbrand 2010).


How the intervention might work

The aquatic environment has particular properties, such as temperature of the water and the humid, pollen-free air. These features have shown extra benefits in people with asthma, facilitating air exchange (Barbosa 2011; Hildenbrand 2010). Water-based exercises have therefore been widely used, as they improve breathing and increase lung volume (Aranđelović 2007). Water-based exercises also stimulate physiological pathways which may raise forced expiratory volume in one second (FEV1) and forced vital capacity (FVC), both of which are objective measures for bronchospasm (Aranđelović 2007). Exercises increase cardiovascular fitness and, consequently, maximal consumption of oxygen (VO2max), reducing the minute ventilation required to exercise and decreasing the stimulus for bronchoconstriction. Regular and long-term exercises may be helpful in asthmatic patients and impact positively on quality of life (Chandratilleke 2012). In addition, during water-based exercises the air inhaled will be humidified, attenuating asthma risks (O'Byrne 2012; Randolph 2009).


Why it is important to do this review

There are Cochrane systematic reviews on physical training (Chandratilleke 2012), breathing exercises (Holloway 2004) and inspiratory muscle training (Ram 2003) for asthma. However, the effectiveness and safety of water-based exercises in people with asthma are unclear. There are no systematic reviews focusing on the relationship between water-based exercises and asthma in adults. In this systematic review we therefore intend to map the scientific literature and describe the evidence on this topic.



  1. Top of page
  2. Background
  3. Objectives
  4. Methods
  5. Acknowledgements
  6. Appendices
  7. Contributions of authors
  8. Declarations of interest
  9. Sources of support

To assess the effectiveness and safety of water-based exercises for asthma in adults.



  1. Top of page
  2. Background
  3. Objectives
  4. Methods
  5. Acknowledgements
  6. Appendices
  7. Contributions of authors
  8. Declarations of interest
  9. Sources of support

Criteria for considering studies for this review


Types of studies

Randomised controlled trials (RCTs) will be included, irrespective of language, age of publication or publication status. Cross-over and cluster-RCTs will be included, however we will analyse the data obtained from them separately.


Types of participants

We will consider participants meeting the following criteria.

  • Adults of either gender
  • Adults with asthma diagnosed according to clinical criteria (American Thoracic Society (ATS), European Respiratory Society (ERS) or British Thoracic Society (BTS)) and other validated diagnostic criteria


Types of interventions

We will include studies which compare any type of water-based exercise to another water-based exercise, land-based exercise or usual care. We will document the duration and frequency of sessions and the overall length of the programme. At least one group in each comparison must use water-based exercise.

The following possible comparisons may be included:

  • Swimming versus hydrogymnastics
  • Swimming versus hydrotherapy
  • Water-based exercise versus land-based exercise
  • Water-based exercise versus usual care


Types of outcome measures


Primary outcomes

  • Quality of life (measured using a validated questionnaire, e.g. Asthma Quality of Life Questionnaire (AQLQ))
  • Exacerbations leading to a course of oral steroids
  • Exacerbations leading to health centre visits
  • Exacerbations leading to hospitalisations


Secondary outcomes

  • Use of rescue medication (e.g. short-acting beta2-agonist (SABA)) or symptom controller (e.g. long-acting beta2-agonist (LABA))
  • Symptoms (as measured on a validated scale (e.g. Lara Asthma Symptom Scale (LASS))
  • Lung function by physiological measures (e.g. spirometry, FEV1, FVC)
  • Reduction in medication usage (e.g. inhaled corticosteroids or leukotriene inhibitors)
  • Adverse events (any reaction due to the water treatment process (e.g. chlorine), exercise induced-bronchoconstriction (EIB))


Search methods for identification of studies


Electronic searches

We will identify trials from the Cochrane Airways Group Specialised Register of trials (CAGR), which is derived from systematic searches of bibliographic databases including the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, EMBASE, CINAHL, AMED and PsycINFO (see Appendix 1 for further details). We will search the CAGR using the strategy in Appendix 2 .We also will search LILACS (Latin American and Caribbean Health Sciences), PEDro (The Physiotherapy Evidence Database), SIGLE (System for Information on Grey Literature) and Google Scholar. We will handsearch the respiratory journals and meeting abstracts of the American Thoracic Society (ATS), European Respiratory Society (ERS) and British Thoracic Society (BTS).

We will check for ongoing studies in: (; the metaRegister of Controlled Trials (mRCT) (; International Clinical Trials Registry Platform (ICTRP) (; Pan African Clinical Trials ( and EU Clinical Trials Register (

We will apply no language or date restrictions. We will search all databases from their inception to the present date.

We will use Endnote X5 to manage the references and exclude duplicate articles found in the different searches.


Searching other resources

We will check the reference lists of all primary studies and review articles for additional references. We will contact the authors of identified trials and ask them to identify other published and unpublished studies. We will also contact exercise equipment manufacturers and experts in the field.


Data collection and analysis

We will perform data collection and analysis according to the recommendations in the Cochrane Handbook for Systematic Reviews of Interventions (Higgins 2011a).


Selection of studies

Two review authors (AJG, VS) will independently screen titles and abstracts of all the potential studies we identify as a result of the search and code them as 'retrieve' (eligible or potentially eligible/unclear) or 'do not retrieve'. We will retrieve the full-text study reports/publications and two review authors (AJG, VS) will independently screen the full text to identify studies for inclusion. We will record the reasons for the exclusion of any ineligible studies. We will resolve any disagreement through discussion or, if required, we will consult a third person (BNGS). We will identify and exclude duplicates and collate multiple reports of the same study so that each study rather than each report is the unit of interest in the review. We will record the selection process in sufficient detail to complete a PRISMA flow diagram and 'Characteristics of excluded studies' table.


Data extraction and management

Two review authors (AJG, VS) will independently extract the data from the primary studies using a standard form (Google Spreadsheet, e.g. developed for this purpose, which includes methods, participants, intervention and outcomes. One review author will transfer data into Review Manager (RevMan 2012). We will double check that data are entered correctly by comparing the data presented in the systematic review with the study reports. A second review author will spot-check study characteristics for accuracy against the trial report.


Assessment of risk of bias in included studies

Two review authors (AJG, VS) will independently assess the risk of bias for each study using the criteria outlined in the Cochrane Handbook for Systematic Reviews of Interventions (Higgins 2011b). Any disagreement will be resolved by discussion or by involving a third author (MSP). We will assess the risk of bias according to the following domains.

  • Random sequence generation (selection bias)
  • Allocation concealment (selection bias)
  • Blinding of participants and personnel (performance bias)
  • Blinding of outcome assessment (detection bias)
  • Incomplete outcome data (attrition bias)
  • Selective reporting (reporting bias)
  • Other bias (other sources of bias related to a particular trial design (cross-over or cluster-randomised) or specific circumstances (interventions mixed))

We will classify the risk of bias as low, high or unclear (Higgins 2011b).


Measures of treatment effect

Considering the proposed objectives of this review, we may use four types of measurements of treatment effect for the primary studies.

  • Dichotomous data: outcomes measures evaluated as binary responses. We will show the summarised results as risk ratio (RR) or odds ratio (OR) and, if necessary, we will calculate the number needed to treat to benefit (NNTB) from the RR or OR. This type of data may be found for the number of acute exacerbations, for example.
  • Continuous data: outcome measures evaluated by numerical quantity. We will combine the results using the mean difference (MD) for measures using the same scale or the standardised mean difference (SMD) where different scales are used to evaluate the same outcome. This type of data may be found for studies measuring quality of life, for example.
  • Count and rates: this measure of effect may mean that exacerbation episodes are counted twice or more in the same person. If a meta-analysis is possible, we may use the risk ratio as it represents the rate of events in the two groups by dividing one by the other.
  • Time-to-event: we may use the hazard ratio to determine when the event happened and its link with the intervention.

If we find more than one study which analyses the same outcome, we will conduct a meta-analysis. All statistical parameters will use 95% confidence intervals (CI) (Deeks 2011).


Unit of analysis issues

We will consider the individual patient to be the unit of analysis. If we include cluster-randomised trials, the unit of analyses will be the group which was allocated the intervention. In cross-over designs we will only include the phase one data to avoid a carryover effect.


Dealing with missing data

We will contact authors of studies by email if the study reports do not report the outcomes measures of interest, do not describe the process of randomisation, do not describe intention-to-treat analysis or are missing any other necessary data. We will send at least two emails to the corresponding author and, if no answer is obtained, we will present and discuss this in the text.


Assessment of heterogeneity

We will assess the inconsistencies between studies using the I2 statistic and describe the percentage of variability in effect. We will consider heterogeneity to be substantial when I2 > 50% (Deeks 2011). If we find substantial heterogeneity among studies, we will explore this with subgroup analysis of study characteristics: participants, interventions, etc.


Assessment of reporting biases

Reporting biases can affect the likelihood of publication and statistically significant results may be selectively reported. It is important that this is assessed because reporting biases may over or under-estimate the treatment effect. If mismatches are identified, we will contact the authors for further information. We also plan to explore the impact of including such studies by conducting a sensitivity analysis. We will perform a funnel plot asymmetry test if we are able to meta-analyse 10 or more trials.


Data synthesis

We will conduct a meta-analyses if the combination of data is possible. We will use a fixed-effect model unless there is substantial heterogeneity (I2 > 50%) where we will choose a random-effects model. We will present the data in forest plot graphics produced by RevMan 5.2. If data combination is not possible, we will describe the individual studies. We also plan to create a 'Summary of findings' table using the methods and recommendations described in Section 8.5 and Section 12 of the Cochrane Handbook for Systematic Reviews of Interventions (Higgins 2011b; Schünemann 2011) and using the GRADEpro software (GRADEpro 2008). We plan to include the following outcomes: quality of life, number of acute exacerbations, level of severity of disease, lung function, reduction in medication usage and adverse events.


Subgroup analysis and investigation of heterogeneity

We will conduct subgroup analysis considering participant and intervention characteristics.

  • Patients

  1. Comorbidities

  • Intervention

  1. Type of exercise (swimming (horizontal), hydrogymnastics (vertical))
  2. Frequency of exercise (how many sessions/week)
  3. Intensity: light (1.6 to 2.9 metabolic equivalents (METs)), moderate (3 to 5.9 METs), vigorous ≥ 6 METs

  • Environmental characteristics

  1. Water temperature and air humidity
  2. Water treatment process (chlorinated versus non-chlorinated)
  3. Water depth


Sensitivity analysis

The sensitivity analysis will help us to understand whether the findings are dependent on the authors' interpretation. We will test studies with limited information to check whether the robustness of the assumptions influences the review findings. Moreover, we will conduct sensitivity analyses with studies at high and unclear risk of bias. We also plan to conduct sensitivity analyses to look at the effects of missing data.



  1. Top of page
  2. Background
  3. Objectives
  4. Methods
  5. Acknowledgements
  6. Appendices
  7. Contributions of authors
  8. Declarations of interest
  9. Sources of support

The authors wish to acknowledge Emma Welsh, Emma Jackson and Julia Walters for their attention and help, and Liz Stovold for building the search strategy. We would like to thank the Cochrane Handbook Study Group from the Brazilian Cochrane Centre for the opportunity to discuss and explore Cochrane methodology.



  1. Top of page
  2. Background
  3. Objectives
  4. Methods
  5. Acknowledgements
  6. Appendices
  7. Contributions of authors
  8. Declarations of interest
  9. Sources of support

Appendix 1. Sources and search methods for the Cochrane Airways Group Specialised Register (CAGR)


Electronic searches: core databases

DatabaseFrequency of search

MEDLINE (Ovid)Weekly

EMBASE (Ovid)Weekly

CENTRAL (The Cochrane Library)Monthly

PsycINFO (Ovid)Monthly





Handsearches: core respiratory conference abstracts

ConferenceYears searched

American Academy of Allergy, Asthma and Immunology (AAAAI)2001 onwards

American Thoracic Society (ATS)2001 onwards

Asia Pacific Society of Respirology (APSR)2004 onwards

British Thoracic Society Winter Meeting (BTS)2000 onwards

Chest Meeting2003 onwards

European Respiratory Society (ERS)1992, 1994, 2000 onwards

International Primary Care Respiratory Group Congress (IPCRG)2002 onwards

Thoracic Society of Australia and New Zealand (TSANZ)1999 onwards



MEDLINE search strategy used to identify trials for the CAGR


Asthma search

1. exp Asthma/

2. asthma$.mp.

3. (antiasthma$ or anti-asthma$).mp.

4. Respiratory Sounds/

5. wheez$.mp.

6. Bronchial Spasm/

7. bronchospas$.mp.

8. (bronch$ adj3 spasm$).mp.

9. bronchoconstrict$.mp.

10. exp Bronchoconstriction/

11. (bronch$ adj3 constrict$).mp.

12. Bronchial Hyperreactivity/

13. Respiratory Hypersensitivity/

14. ((bronchial$ or respiratory or airway$ or lung$) adj3 (hypersensitiv$ or hyperreactiv$ or allerg$ or insufficiency)).mp.

15. ((dust or mite$) adj3 (allerg$ or hypersensitiv$)).mp.

16. or/1-15


Filter to identify RCTs

1. exp "clinical trial [publication type]"/

2. (randomised or randomised).ab,ti.

3. placebo.ab,ti.

4. dt.fs.

5. randomly.ab,ti.

6. trial.ab,ti.

7. groups.ab,ti.

8. or/1-7

9. Animals/

10. Humans/

11. 9 not (9 and 10)

12. 8 not 11

The MEDLINE strategy and RCT filter are adapted to identify trials in other electronic databases.


Appendix 2. Search strategy for Cochrane Airways Group Register


#2 MeSH DESCRIPTOR Asthma Explode All

#3 asthma*:ti,ab

#4 #1 or #2 or #3

#5 MeSH DESCRIPTOR Water Explode All

#6 MeSH DESCRIPTOR Swimming Pools

#7 water*

#8 aquatic*

#9 immers*

#10 bath*

#11 whirlpool*

#12 pool*

#13 hydro*

#14 #5 or #6 or #7 or #8 or #9 or #10 or #11 or #12 or #13

#15 exercis*

#16 gym*

#17 aerobic*

#18 anaerobic*

#19 breathing*

#20 endurance*

#21 train*

#22 kinesiotherap*

#23 isokinetic*

#24 isometric*

#25 treadmill*

#26 muscle*

#27 muscular*

#28 pilates*

#29 plyometric*

#30 resistance*

#31 stretch*

#32 posture*

#33 movement*

#34 motion*

#35 physiotherap*

#36 physical*

#37 fitness*

#38 sport*

#39 walk*

#40 run*

#41 calisthenic*

#42 MeSH DESCRIPTOR Physical Therapy Modalities Explode All

#43 MeSH DESCRIPTOR Exercise Explode All

#44 MeSH DESCRIPTOR Sports Explode All

#45 MeSH DESCRIPTOR Gymnastics

#46 MeSH DESCRIPTOR Exercise Therapy

#47 #15 or #16 or #17 or #18 or #19 or #20 or #21 or #22 or #23 or #24 or #25 or #26 or #27 or #28 or #29 or #30 or #31 or #32 or #33 or #34 or #35 or #36 or #37 or #38 or #39 or #40 or #41  or #42 or #43 or #44 or #45 or #46

#48 #14 and #47

#49 hydrotherap*

#50 swim*

#51 hydrogymnastic*

#52 aqua-aerobic*

#53 "aqua aerobic*"

#54 aquafit*

#55 dive* or diving

#56 hydrokinetic*

#57 hydro-kinetic*

#58 "Ai Chi"

#59 Halliwick

#60 balneotherap*

#61 MeSH DESCRIPTOR Hydrotherapy

#62 MeSH DESCRIPTOR Swimming

#63 MeSH DESCRIPTOR Balneology Explode All

#64 #49 or #50 or #51 or #52 or #53 or #54 or #55 or #56 or #57 or #58 or #59 or #60 or #61 or #62 or #63

#65 #48 or #64

#66 #4 and #65

(MISC1 = field in the Register where each record is coded for disease, e.g. AST = asthma)


Contributions of authors

  1. Top of page
  2. Background
  3. Objectives
  4. Methods
  5. Acknowledgements
  6. Appendices
  7. Contributions of authors
  8. Declarations of interest
  9. Sources of support

Co-ordination of the protocol: Antonio Jose Grande.

Searching for studies to conceptualise background: AJG, VS, BG.

Planning the methods section, drafting the review and approving the final version of the protocol: AJG, VS, BG, RR, SAP, MSP.

Antonio Jose Grande is the guarantor of the protocol.


Declarations of interest

  1. Top of page
  2. Background
  3. Objectives
  4. Methods
  5. Acknowledgements
  6. Appendices
  7. Contributions of authors
  8. Declarations of interest
  9. Sources of support

None known.


Sources of support

  1. Top of page
  2. Background
  3. Objectives
  4. Methods
  5. Acknowledgements
  6. Appendices
  7. Contributions of authors
  8. Declarations of interest
  9. Sources of support

Internal sources

  • None, Not specified.


External sources

  • None, Not specified.


Additional references

  1. Top of page
  2. Abstract
  3. Background
  4. Objectives
  5. Methods
  6. Acknowledgements
  7. Appendices
  8. Contributions of authors
  9. Declarations of interest
  10. Sources of support
  11. Additional references
Ambrosini 2010
  • Ambrosini AB, Brentano MA, Coertjens M, Kruel LFM. The effects of strength training in hydrogymnastics for middle-age women. International Journal of Aquatic Research and Education 2010;4:153-62.
Aranđelović 2007
  • Aranđelović M, Stanković I, Nikolić M. Swimming and persons with mild persistant asthma. The Scientific World Journal 2007;7:1182–8.
Avelar 1999
  • Avelar NCP, Bastone AC, Alcantara MA, Gomes WF. Effectiveness of aquatic and non-aquatic lower limb muscle endurance training in the static and dynamic balance of elderly people. Revista Brasileira de Fisioterapia 2010;14:3229-36.
Banzett 1985
  • Banzett RB, Lansing RW, Reid MB. Reflex compensation of voluntary inspiration when immersion changes diaphragm length. Journal of Applied Physiology 1985;59(2):611–8.
Barbosa 2011
  • Barbosa TM, Marinho DA, Reis VM, Silva AJ, Bragada JA. Physiological assessment of head-out aquatic exercises in healthy subjects: a qualitative review. Journal of Sports Science and Medicine 2009;8:179-89.
CDC 2011
  • Centers for Disease Control and Prevention. Asthma surveillance data. (accessed November 12, 2012).
Chandratilleke 2012
Corbin 2011
  • Corbin CB. Concepts of Fitness and Wellness: a Comprehensive Lifestyle Approach. McGraw Hill, 2011.
Deeks 2011
  • Deeks JJ, Higgins JPT, Altman DG. Chapter 9: Analysing data and undertaking meta-analyses. In: Higgins JPT, Green S editor(s). Cochrane Handbook for Systematic Reviews of Intervention. Chichester: John Wiley & Sons, 2011.
Denning 2012
  • Denning WM, Bressel E, Dolny D, Bressel M, Seeley MK. A review of biophysical differences between aquatic and land-based exercise. International Journal of Aquatic Research and Education 2012;6:46-67.
Gonçalves 2008
  • Gonçalves RC, Nunes MPT, Cukier A, Stelmach R, Martins MA, Carvalho CRF. Effects of an aerobic physical training program on psychosocial characteristics, quality-of-life, symptoms and exhaled nitric oxide in individuals with moderate or severe persistent asthma. Revista Brasileira de Fisioterapia 2008;12(2):127-35.
Goodman 2008
GRADEpro 2008
  • Brozek J, Oxman A, Schünemann H. GRADEpro. 3.2 for Windows. GRADE group, 2008.
Higgins 2011a
  • Higgins JPT, Deeks JJ. Chapter 7: Selecting studies and collecting data. In: Higgins JPT, Green S editor(s). Cochrane Handbook for Systematic Reviews of Interventions. Chichester: John Wiley & Sons, 2011.
Higgins 2011b
  • Higgins JPT, Altman DG. Chapter 8: Assessing risk of bias in included studies. In: Higgins JPT, Green S editor(s). Cochrane Handbook for Systematic Reviews of Interventions. Chichester: John Wiley & Sons, 2011.
Hildenbrand 2010
  • Hildenbrand K, Nordio S, Freson TS, Becker BE. Development of an aquatic exercise training protocol for the asthmatic population. International Journal of Aquatic Research and Education 2010;4:278-99.
Holloway 2004
Lucas 2005
Malkia 1998
O'Byrne 2012
  • O'Byrne PM. Exercise-induced bronchoconstriction. In: Basow DS editor(s). UpToDate. Waltham, MA: UpToDate, 2012.
Pedersen 2006
Ram 2003
  • Ram FSF, Wellington SR, Barnes NC. Inspiratory muscle training for asthma. Cochrane Database of Systematic Reviews 2003, Issue 3. [DOI: 10.1002/14651858.CD003792]
Randolph 2009
RevMan 2012
  • The Nordic Cochrane Centre, The Cochrane Collaboration. Review Manager (RevMan). 5.2. Copenhagen: The Nordic Cochrane Centre, The Cochrane Collaboration, 2012.
Schünemann 2011
  • Schünemann HJ, Oxman AD, Vist GE, Higgins JPT, Deeks JJ, Glasziou P, et al. Chapter 12: Interpreting results and drawing conclusions. In: Higgins JPT, Green S editor(s). Cochrane Handbook for Systematic Reviews of Interventions Version 5.1.0 (updated March 2011). Chichester: John Wiley & Sons, 2011.
To 2012
  • To T, Stanojevic S, Moores G, Gershon AS, Bateman ED, Cruz AA, et al. Global asthma prevalence in adults: findings from the cross-sectional world health survey. BMC Public Health 2012;12:204.
WHO 2011
  • World Health Organization. Chronic respiratory disease. Asthma definition. 2011; Vol. (accessed November 12, 2012).