Are studies that employ convenience sampling invalid

Sampling
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Sampling
Introduction
Once a researcher has identified and defined the target study population, the next step is to select a sample from the population through the sampling process. In research, sampling is defined as the process of selecting a subset of the entire population for study so that the researcher can determine the characteristics of the whole population without having to go around investigating every individual within the target population (Cochran, 2007). It applies to studies in which the researcher chooses to study a portion of the objects/elements in the target population and generalize their inferences to the entire population, rather than studying all elements. A researcher should exercise caution when selecting a sample because inappropriate sampling may lead to bias, defunct the whole process, and exclude important data (Cochran, 2007). There are several sampling methods in research. The methodology used to sample is dependent on the type of analysis being done by the researcher.
Sampling Terminologies
Sample: It is a group of individuals or subjects that has been selected by the researcher to represents the larger population.
Sample frame: This refers to a list of elements or items used by the researcher to select a sample within the target population.
Population: It refers to an entire pool from which a sample is selected. Therefore, it is a group of people, events, objects, or measurements grouped for a common feature.
Data: It refers to a set of qualitative and quantitative variables about objects, an individual, or more persons.
Why Sampling Frame is the Most Critical Element of Study’s Sampling Plan
The sampling frame is conceivably the paramount prerequisite for a good sampling plan of any study. That’s because it enables the researcher to identify every single element of the target population and include in the sample (Cochran, 2007). For instance, when a researcher wants to study the working condition of an organization that has a population of 1000 employees, the sampling frame, in this case, is the HR's database, which gives a list of the employees' names, contact details, and their departments. Therefore, the sampling frame is paramount during research since it provides extra information about the elements that improve the study project when related to the group of interest. The sampling frame also accomplishes the comprehensiveness and precision of the research study.
How Poor Specification of the Sampling Frame Forestalls the Research Process
A sampling frame that is poorly specified can result in frame errors that do not give an accurate and comprehensive representation of the population being targeted by the researcher (Bunte et al., 2001). Below are some of the frame errors and explanations on how each of them forestalls the research process.  
1 Duplicate entries
These occur when some target population members appear in the sample frame more than once, increasing their chances of being sampled. That will affect the replicability and the interpretation of the results during the research process.
2 Missing elements
It i...