Practical factors relate to time, money, skills and logistics. Longitudinal studies may be time consuming and costly. The sociologist may not have the skills for the research, such as in an interview. They may not be able to take part due to characteristics, such as being the opposite gender. Logistics- the researcher may choose secondary sources if investigating the past. Interviews are possible, but rely on memory. Sample size- a large sample would fit questionnaires or official statistics better. The nature of the group may be difficult, some groups such as gangs may refuse to answer.