Noticing shifts in style
Although a recorded interview tends to make people rather self-conscious about their speech, you may still notice some shifts in their speech style when the circumstances or the mood change slightly. This is similar to the way in which bilingual speakers may change languages in the middle of a conversation. Here are just a few examples from the Doyle family interview:

When people get excited about a particular topic
When Karen starts to talk about what happened to her daughter’s accent during their recent holiday in the USA, she clearly warms to her topic and is particularly relaxed, resulting in some forms of speech (such as the use of ‘like’ to introduce direct speech) that she doesn’t use elsewhere in the interview.

Similarly, when Stephen gets involved in talking about ‘attractive’ girls, he produces an informal double negative ‘Can’t think of nothing else’ when he has only moments previously used the more standard form ‘Can’t think of any more’.

When people are mimicking someone else’s speech
When Karen mimics her daughter saying ‘Hey Mom’, she does this in a deliberately American accent. Similarly, when Peter mimics the people in the pub in Widnes, he does does this in his his best imitation of their speech: “I don’t know what you are going on about, I don’t know what you are saying”.

When Stephen tells Jodie how he would describe the interview to his mates, he effectively mimics his own speech in a very different context: ‘I was sitting in this house with this bird and she had a microphone and she was nattering on asking me all these questions and I was just saying, like, for instance, “What would you say for hot?” “Roasting”. And it was, ah, mad you know lah’. Apart from changes in his pronunciation and speed of speech (which is rather more drawn out than his speech elsewhere in the interview), Stephen also uses words like ‘bird’ and ‘nattering’ which do not appear elsewhere and other indicators of informal speech like the filler ‘like’ or the discourse particles ‘ah’ and ‘lah’.

When you examine your own data, be careful to consider (and keep a record of) the context in which people say things, and whether the language they use at one point in the interview is typical or atypical of what they do more generally. Good luck...