An element refers to a unit about which the researcher is interested in collection information with reference to. The main role of an element during a research study is to provide a basis for the collection and analysis of data. Elements usually provide information relating to the entire population. An example of an element is a group of inmates with has unique characteristics or attributes, for instance, male inmate who is suffering from HIV/AIDS and drug abuse. Elements are also referred to units of analysis.
Population
A population refers to a group of individuals or set of items with the desired characteristics that the researcher would like to examine, analyze and understand. It is a set of all the subjects or entities that the researcher wants to study. A population is an inclusive aggregation of the elements used in a research study. Schutt and Bachman define a population as a collection or cluster of identical elements. The main role of the population is to provide a set of items from which the sample population can be selected or chosen. Thus, a population provides a subpopulation, subset or sample population that is used by the researcher for sampling purposes during the research study. An example of a population is all prisoners in Federal jails in the United States of America.
Study Population
A study population refers to a group of individuals or a set of subjects of study. The study population must be of great interest to the researcher. In my opinion, a study population is a group or set of identical items or subjects of study that the researcher chooses to examine due to their relevance to the research topic or question. For example, a researcher who wants to study crimes committed by juveniles would select child prisoners aged below fourteen years as the study population. The main role of a study population is to provide the researcher with reliable and accurate information that is relevant to the research questions. In my view, study populations must also have comparable characteristics that are definable and examinable by the researcher, for example, age, gender and level of education of juvenile offenders within the criminal justice systems.
Random Selection
Random selection refers to the process of choosing or picking the subjects for a research study indiscriminately or in an unsystematic manner. The main purpose of random selection is to give all members of the population equal and independent chances for being included in the sample or study population. Random selection permits indiscriminate selection of elements to be used during the study. Maxfield and Babbie also emphasize that random selection provides all members of the population with equal chances of inclusion in the sample population to be used during the research study. In my opinion, random selection also increases external validity of the study thus resulting into dependable and legitimate generalization of findings of the research. It also increases chances of better representation of the members of the population in the sample population by eliminating biasness of the researcher during sampling.
Sampling Unit
A sample unit is a single element chosen from the target population for assessment purposes during the research study. For example, in a study of criminal justice among juvenile offenders, a single child is considered a sampling unit. According to Dattalo, a sampling unit could also be a group of elements in a population that the researcher uses for choosing members of the sample population,.For instance, a household of consumers could be considered as a sampling unit during marketing researches. Sampling units usually share common characteristics thus provide the researcher with invaluable information that is useful for drawing conclusions during the research study.
Statistic
A statistic is a summary of descriptions for a particular variable in a sample population. The main function of a statistic is to measure specific traits, qualities or characteristics of a sample population.
Parameter
A parameter is a summary of descriptions given within the population. A parameter is usually used to measure variables of the entire population.
Advantages of Probability Sampling over Non-Probability Sampling
Probability sampling refers to a type of sampling technique in which all members of the population have equal chances of being selected. According to Som, selection of elements from the population during probability sampling is usually based on specific random formulae.
In my opinion, the main advantage of probability sampling is that it allows fairness and equality during the selection of elements of the sample population during a study. All elements or subjects of study are given equal chances of being picked. Secondly, sample populations created through probability sampling are highly representative especially when all subjects in the target population participate during the sampling process.
Thirdly, probability sampling is convenient for use where a large population of the study elements is required. It also helps in increasing the external validity of the research study. Besides, probability sampling also helps in minimizing systematic biasness of the researcher towards any participant in the study. This helps to increase the reliability of the research study.
The Last but not least, probability sampling permits minimization of constraints used during identification and selection of participants of the research. This helps to simplify the sampling process as well as to achieve a higher rate of recruitment and retention of the research participants.