References
- Lancaster GA, Dodd S, Williamson PR. Design and analysis of pilot studies: recommendations for good practice. J Eval Clin Pract. 2004;10(2):307–12.10.1111/jep.2004.10.issue-2
- Thabane L, Ma J, Chu R, et al. A tutorial on pilot studies: the what, why and how. BMC Med Res Methodol. 2010;10(1):1–15.10.1186/1471-2288-10-1
- Van Teijlingen E, Hundley V. The importance of pilot studies. Nurs Stand. 1998;16(40):747–55.
- Nriagu J, Robins T, Gary L, et al. Prevalence of asthma and respiratory symptoms in south-central Durban, South Africa. Eur J Epidemiol. 1999;15(8):747–55.10.1023/A:1007653709188
- Phaswana-Mafuya N, Peltzer K, Chirinda W, et al. Self-reported prevalence of chronic non-communicable diseases and associated factors among older adults in South Africa. Glob Health Action. 2013;6(20936):1–7.
- Recommended respiratory disease questionnaires for use with adults and children in epidemiological research. 1978 [cited 2015 Sep 22]. Available from: www.thoracic.org.
- Statistics South Africa: statistical release (Revised) Census 2011. 2012 [cited 2015 Sep 23]. Available from: www.statssa.gov.za.
- DeVellis RF. Scale development: theory and applications. Appl Soc Res Meth Series. Sage C, Chapel Hill, USA: University of Carolina; 1991. p. 115205.
- Torres-Reyna O. Getting started in factor analysis (using Stata 10). Princeton, NJ: Data and Statistical Services; 2012 [cited 2015 Jul 21]. Available from: http://dss.princeton.edu/training/Factor.pdf.
- Shaikh S, Nafees AA, Khetpal V, et al. Respiratory symptoms and illnesses among brick kiln workers: a cross sectional study from rural districts of Pakistan. BMC Pub Health. 2012;12(999):1–9.
- Comstock GW, Tockman MS, Helsing KJ, et al. Standardized respiratory questionnaires: comparison of the old with the new. Am Rev Respir Dis. 1979;119(1):45–53.