Most measurements of happiness are by standardized questionnaires or interview schedules. It could also be done by informed observers – those who know the individual well and see them regularly. There is also experience sampling, where people report how happy they are many times a day. Yet, another form of measurement is to investigate a person’s memory and check whether they feel predominantly happy or unhappy about their past. Finally, there are some crude but ever-developing physical measures looking at everything from brain scanning to saliva levels.