Studies have found that children who learn musical instruments tend to have larger vocabularies and better reading comprehension than children who do not. This relationship has been observed across multiple countries and socioeconomic groups. Music education clearly enhances language development. The explanation is straightforward: learning music trains the brain to recognise patterns and structures, skills that directly transfer to language processing. Some researchers have suggested that perhaps children with better language abilities are simply more likely to persist with music lessons, but this cannot be correct because the vocabulary differences are observed even among children who have only studied music for six months. Schools that have cut music programmes to save money are therefore undermining their students' literacy development. Which one of the following best identifies the flaw in the above argument?