Answer:
a) The population is the 1,500 employees, while the sample is the 60 female and 80 male employees selected using proportional allocation.
b) The scope of data collection is a sample survey, as only a subset of the population is being studied.
c) The variable of interest is the average monthly income of the employees.
d) The possible sources of data collection could include surveys or interviews of the selected employees, or obtaining salary data from the human resources department of the company.
e) The type of statistics used would be inferential statistics, specifically confidence interval estimation and hypothesis testing, to make inferences about the population based on the sample data.