Purposive sampling strategy.
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*These include asthma, chronic obstructive pulmonary disease or bronchitis, heart disease, kidney disease, liver disease, neurological conditions, weakened immune system due to conditions such as HIV and AIDS, or as a result of medication such as steroid tablets or chemotherapy.**A = higher socio-economic group and E = lower socio-economic group. We used occupation and income data to determine participants' social grade.Purposive sampling strategy.
创建时间：
2015-12-02
