We would like to measure the influence of the use of social media on lifestyle (e.g. sport, nutrition, consumer behaviour). Do you know of similar research and approaches?
As this seems to be a multivariate study I suggest you use the SEM analysis .Here we start first with the review of literature which shows the impact of social media on each of these variables of lifetsytle namely e.g. sport, nutrition, consumer behaviour.In case you find past review where it does say that social media does effect any of these variables,then we construct a proposed model.For each of this variable you will need a scale(list of statements to measure these variables).For example a scale of nutrition will consist of statements on Likert scale which measure a person's nutrition .These scales are generally available from the research papers which you study to find the impact of social media on lifestyle.We then do a SEM analysis to see the overall impact of the same on the lifestyle of the person.Read one of my papers on my research gate profile.You will get an idea of how to do a multivariate analysis like this one