Reason: There are only 2 sources of data-primary and secondary data.
Reason: The data collected by investigator is called the primary data.
Reason: Non-random selection of items obstructs the equal chance of every item of the Universe of getting selected. Hence, the certain bias are involved.
Reason: If the field of investigation or the population size is large then the possibility of non-sampling increases.
Reason: This method is only suitable for the illiterate population spread of a large area.
OI Prii MARK KARO BEST!! NOHOLE KINTU MAARIM!! :P