Little brother. My brother came along at an age where I was probably the most likely to make my mind up about smoking. I was around 11 or 12 years old and I had a lot more exposure from my friends.. but then once he came along and my mum stopped, there was just none around the house. It helped reinforce the decision not to smoke. (Female, non-smoker, 17 years).
Johnston et al. BMC Public Health 2012 12:963 doi:10.1186/1471-2458-12-963