What is the difference between a representative sample and a random sample?

What is the difference between a representative sample and a random sample?

In principle, a large enough random sample will be a representative sample, the majority of the time. This is based on scientific and mathematical principles, ultimately derived from probability theory.

However, this assumes that the sample is large enough, is drawn from a representative sample frame, and is properly randomized. It also assumes that there isn’t any bias introduced by the tendency of some groups to be more or less willing to be surveyed than other groups and that there is no systematic reason to think that some groups were missed in the sampling. Quite a few qualifiers there, especially in this era of sample fatigue (i.e. people get tired of being surveyed due to the large number of surveys being done, since it now relatively cheap and easy).

When you hear the term, “a representative sample”, that generally means some testing has been done on the survey results, to confirm that the survey respondents have similar proportions of members from critical groups as the population at large, or at least the population that is considered relevant to the survey’s overall purpose.

It can also mean that special efforts have been made to ensure that the survey will be representative of the relevant population, in some particularly important way, via survey design (e.g. cluster sampling, stratified sampling). In those cases, the phrase “representative” might actually mean “non-representative” (e.g. if you want to ensure that certain smaller but important groups are over-sampled).

In either case, the checking for representative proportions can either be informal (it looks like we got about as many males as females) or a rigorous formal inferential statistical process (in a respondent group of this size, from a sample of some other size, we should expect between x1 and x2 females, 19 times out of 20).

Since there are dozens of ways to measure whether a respondent group is representative (gender, age, ethnic background, educational background, socioeconomic status, language, religion, etc.) these post-survey checks can never really be certain of guaranteeing a representative sample.

That’s why a large, randomly drawn, high response rate survey is the gold standard for survey research, but it is very difficult to achieve in practice.

But note that random sampling is not appropriate for many endeavors in life:

  

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And, as always, you should think about taking a break and reading an adventure/romance story (or the entire series). 

The Witches’ Stones Book 1: Rescue from the Planet of the Amartos

 So, go on a romantic science fiction adventure with an agent of Earth’s Terra Federation’s counter-intelligence group “The Agency”, to prevent the mystical and powerful Witches’ Stones from falling into the hands of the shadowy power-mad developing galactic empire, known to Earthlings only as The Organization.  Key to this mission is the rescue of an apparently unassuming Earth girl, who holds the key to the galactic balance of power, via her ability (unknown to her) to psychically unlock the energies of the Witches’ Stones. 

Amazon U.S:  https://www.amazon.com/dp/B008PNIRP4

Amazon U.K.: http://www.amazon.co.uk/gp/product/B008PNIRP4

Amazon Canada: https://www.amazon.ca/dp/B008PNIRP4

Amazon Germany: https://www.amazon.de/dp/B008PNIRP4

Amazon Australia: https://www.amazon.com.au/dp/B008PNIRP4

Amazon Japan: https://www.amazon.co.jp/dp/B008PNIRP4

Amazon India: https://www.amazon.in/dp/B008PNIRP4

Amazon Spain: https://www.amazon.es/dp/B008PNIRP4

 Amazon France: https://www.amazon.fr/dp/B008PNIRP4

Witches’ Stones Book One – Rescue from the Planet of the Amartos

Sarah Mackenzie had trained as a space ship mechanic at the Space Port of her home city on Earth. She left Earth to explore the galaxy, and, some months later, landed a dream assignment, to become the ship mechanic of an Explorer ship, the Beth 117.

The Beth was on its way to a planet at the edge of the galaxy, where its crewmembers were to search for the Witches’ Stones, or amartos, the mysterious crystals, which the Witches of the world, Kordea, use to channel and augment their psychic energies.

Sarah has no idea that she, herself, happens to be Stone-sensitive, just like the Witches are. Under perilous circumstances, she comes across the cache of the Stones which the Explorers are looking for, and, unwittingly, “keys” them, igniting a psychic blaze that attracts the attention of The Organization, the implacable foe of the Terra Confederation, the centuries-old star-spanning government of most of the human race, and its non-human allies. To make use of amarto-energy, The Organization needs, not just the Stones, but also amarto-sensitive individuals whom they enslave to the devices which they have developed in their pursuit of galactic domination. Thus, they want not just the cache of Stones; they also want Sarah.

To forestall galactic war, rescuers, from a counter-intelligence group, known as The Agency, are sent to the Planet of the Amartos. A fast scoutship, manned by an Agent and a Pilot, must try to fetch Sarah and the amartos, bringing them to a safe haven among the Kordean Witches.

Sarah, herself, has to deal with serious conflicts. In the psychic realm she must choose between The Organization and the Kordean Witches, while retaining mastery over her own mind. In the physical reality, she has become the centre of an armed battle between the Terran scoutship and a military task force sent by The Organization to capture her and the Stones. Her determination to keep control of her own self sends her into unexplored mental realities, while exciting but dangerous physical events swirl around her and the crew of the scoutship, Camin.

To further complicate things, she senses within herself, the beginnings of an attraction to the handsome Agent sent to rescue her. However, she’s merely a naive young woman from Earth; surely, her hopes are beyond realization....

The novel is about 100,000 words, or 250 pages. It is the first book in the Witches' Stones series, which explores the struggle for power among the Terra Confederation, the Kordean Witches and The Organization, as well as the personal and romantic entanglements of the characters. Book 2  and Book 3 complete the series.