critically discuss how each of the attached primary sources might help up us understand and test the push-pull theory?

In her study of the sources available for understanding the motivations of why migrants left their homes in the in the nineteenth century Charlotte Erickson wrote that published migrant letters on the whole were characterised by consistent and blatant bias, whether for or against migration. Erickson argued that to understand migration it was necessary to explore other documents. Essay question: utilising the secondary sources listed below, critically discuss how each of the attached primary sources might help up us understand and test the push-pull theory? SECONDARY SOURCES: -Charlotte Erickson, ‘Introduction’ in Charlotte Erickson, Leaving England: Essays on British Emigration in the Nineteenth Century, (Ithaca, Cornell University Press, 1994). -Dudley Baines, Problems in the History of European Emigration, Chapter 1 in D.E. Baines, Emigration From Europe 1815-1930, Macmillan, London, 1991