Random Sampling Bias

Simple random sampling is when every subject of the sample size representing the population has the same and equal opportunity of being chosen. Incorporating randomness and an equal likelihood of selection is quite difficult for a human, for he or she is naturally prone to bias (whether on purpose or without knowledge and desire). Placing names in a slip of paper and them mixing them around in a box is not as random as we believe or expect it to be. In fact, the act of such method brings its bias because it is a human controlling the selection; the mixing could possibly not be thorough enough, affecting unfairly the probability of a name being picked as opposed to another. This process could also become unreasonable, time consuming and expensive

It does not matter the precautions or other characteristic guidelines followed to insure a reliable and well-conducted survey if the sample was chosen unfairly and without equal chance of selections for all possible candidates. The following are specific sources where bias can be found. Household bias is when members of lager households are unfairly held with higher significance by pollsters. This occurs when they tend to not be fully represented because only one member of a big or small household takes part in the sample. Nonresponse bias usually plays a factor in questionnaires that are sent out by mail, for the percentage of responses obtained is significantly low; not to mention, there is never certainty in the population receiving and taking it. As previously stated, people deny, ignore, or are unavailable to obtain and complete the response; mailed questionnaires do not have the luxury of caller ID and an answering machine. To increase the response rate, rewards must be offered (most of the time being money) and follow-ups or back-up contacts must be available; a higher response rate is more likely when using short and simple phrased surveys. On the other hand, response bias occurs when people refuse to answer truthfully during interviews and questionnaires in fear of their opinions being disreputable and unpopular. Quota sampling bias happens when those conducting interviews have free will and can select the people they will be questioning; in choosing a specific percentage of people based on gender, race, etc. is not a form of giving an equal opportunity to all which is, therefore, bias. Selection bias comes when choosing specific people and not others, which involves not providing an equal chance of