A Swedish study compared the child birth records of 2410 women who had worked as hairdressers to 3462 women from the general population. The hairdressers were found to have a slightly higher proportion of children born with birth defects. Can we conclude that working as a hairdresser causes higher rates of birth defects? Select an answer and submit. For keyboard navigation, use the up/down arrow keys to select an answer. a No, the samples were not selected at random. If we had compared random samples, then we could make this conclusion. b Yes, this study was an experiment which allows us to make causal conclusions. c No, this study was an observational study, and may be subject to the effects of lurking variables. d Yes, the size of the samples means that the study conclusion is reliable