Longitudinal studies collect a great
deal of information through questionnaires. An interviewer might ask
questions either face-to-face, or over the phone, or the participants might
complete the questionnaire on their own. Assessments can be used to show how
study members think, and how their cognitive ability is developing, or
declining over time. These exercises usually take the form of questions, or a set of activities to assess numeracy, literacy, and problem-solving. Many studies ask participants to take part in health assessments. They might measure the height and weight of study members, or examine lung and heart function. Studies are increasingly interested in participants mental health and well-being, and ask questions to assess people’s state of mind. Several studies collect biological samples, such as blood or saliva. Genetic information can be extracted from these samples and the samples can also provide measures of people’s health known as biomarkers.