## Sampling by a defined procedure. The elements of

Sampling

1.          In probability the theory and statistics
is a sequence or other collection of the random variables which is independent
and identically distributed. If each random variable has the same probability
distribution as others. All are mutually independent.

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2.           A sample is a smaller and manageable version
of a larger group. It is a subset containing characteristics of the larger population.  Samples are those which are used in
statistical testing when population sizes are to large for test to include all
possible members.

3.
In statistics and quantitative research methodology, a data sample is a set of data collected and/or
selected from a statistical population by a defined procedure. The elements of
a sample are known as sample points, sampling units or observations.

Importance of the sample

One of the most important
factors that determines if you produces accurate results is your sample. A
sample, by its definition, and it is a subset of the population you are
studying that is selected for the actual study research. Performance of your
research with wrong sample, or just once that is inaccurately designed, and you
will almost certainly get misleading results (in the industry this is called external
validity–the extent to which your sample’s results can
generalize to the population you care about).

I bring up this because I am
seeing more and more surveys where anyone can respond, and can often respond
multiple times. Recently, I’ve seen several online surveys with no
participation restrictions (and not just the fun opinion polls) and email
snowball samples (a snowball sample is one in which additional respondents are
recruited from referrals from initial respondents). I was going to post the
survey links here until I realized I would only be contributing to their poor
results.

These ranged from usage
and opinions of outdoor hiking areas; an economic impact study on the impact
that access to a rock climbing area produces; and a public opinion survey
on criminals. In each example, the survey would have most likely gone to only
those with strong opinions, and in some cases, only those with an opinion that
they wanted to hear anyway. Not to mention, anyone who wanted to could take the
survey multiple times with little effort. The best sampling is one in which all
respondents in your study population have an equal chance of being chosen to
participate and limits respondents to those that you chose.

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