1. Primary data is much more reliable than secondary data. This is because primary data gives up-to-date information about a topic and is collected by doing research, avoiding the use of secondary sources which may include false and not up-to-date information.
2. The most common methods of collecting primary data are interviews, field observations, self-administered surveys, and experiments.
The experimental method:
merits:
-the researcher can have control over variables
-gains insight into methods of instruction
-can be used to determine what's best for the population
demerits:
-sample may not be representative
-human response can be difficult to measure
-subject to human error
---------------
5. Some precautions that should be considered when using secondary data are:
Reliable agency:
-must ensure that the agency that has published the data should be reliable
Method of collecting data used:
-The investigator should also be aware of the method that was used in collecting the data
-Sampling method may be biased depending upon the mode of selection of samples.
-All these should be ascertained before making use of the secondary data.
Suitability for the purpose of an enquiry:
-The Investigator must ensure that the data are suitable for the purpose of the present enquiry.
-The suitability of the data is determined by investigating the nature, objectives, time of collection, etc. of the secondary data.
Adequacy and accuracy to avoid the impact of bias:
-It is necessary to use adequate data to avoid biases and prejudices leading to incorrect conclusions.
---------------
Sorry, I didn't answer all of your questions, but I hope this helps.