## 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.

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.