disadvantage - invalid because document could be inauthentic eg missing pages or if it’s a copy (eg so-called Hitler diaries were proven fake). document may not be what it claims to be
disadvantage - low representativeness because illiterate lower classes are less likely to keep diaries = their accounts are under-represented compared to educated people
advantage - interpretivists = personal documents = good, can get more detailed insights due to first person narrative to draw meaningful conclusions of social behaviour
advantage - positivists = public documents = good, produces numerical and statistical data which can be graphed and studied to establish causes and effects. sociology = science
