what is the concept of sample in research methodologyrelated to research methodology

First, it is usually too costly to test the entire
population..The second reason to sample is that it may be impossible to test the entire
population.The third reason to sample is that testing the entire population often
produces error. Thus, sampling may be more accurate. Perhaps an example will help
clarify this point. The final reason to sample is that testing may be destructive. It
makes no sense to lesion the lateral hypothalamus of all rats to determine if it has an
effect on food intake. We can get that information from operating on a small sample of
rats. Also, you probably would not want to buy a car that had the door slammed five
hundred thousand time or had been crash tested.

The first
sampling procedure is convenience. Another form of sampling
is the simple random sample. A systematic
sample is conducted by randomly selecting a first case on a list of the
population and then proceeding every Nth case until your sample is selected. This is
particularly useful if your list of the population is long. Stratified
sampling makes up the fourth sampling strategy. In a stratified sample,
we sample either proportionately or equally to represent various strata or
subpopulations. Cluster sampling makes up the final
sampling procedure. In cluster sampling we take a random sample of strata and then
survey every member of the group.