2 coments each one 150 words (CITATION AND REFERENCE)

Sampling theory is part of research and how samples are taken in order to conduct an experiment or a type of clinical trial. There are two major categories of sampling methods, one is probability sampling methods where all subjects in the target population have equal chances to be selected in the sample (Shorten & Moorley, 2014). The other is non-probability sampling methods where the sample population is selected in a non-systematic process that does not guarantee equal chances for each subject in the target population. Samples which were selected using probability sampling methods are more representatives of the target population ( Shorten & Moorley, 2014). An example for this would be simple random sampling. For example choosing randomly from a group of people to conduct a study on the effects of tobacco use from a group of those people who use tobacco and have a history of over ten years of smoking. From that group it can be specifically subject to only males and within a certain age gap in order to make the study more efficient. 
Generalizability can be defined as the extension of research findings and conclusions from a study conducted on a sample population to the population at large (Generalizability, 2020). When it comes to nursing research it can help by being able to form some type of idea or hypotheses from a sample that was conducted from a research. This way one can have an idea of what the probability that something will work will actually be effective.
References:
A Shorten, C Moorley. Selecting the sample. Evid Based Nurs. 17(2014) eb–2014–101747–. doi:10.1136/eb-2014-101747. Retrieved from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5325924/#B2
Generalizability. (2020). Generalizability and Transferability. Retrieved from https://writing.colostate.edu/guides/guide.cfm?guideid=65

Sampling theory is the thought process of having a generalized population in mind to conduct a research project that fits the appropriate research the person has in mind. By using this theory when it comes to research, it can be very beneficial with structure and the appropriate study sampling with choosing the appropriate subjects according to the picot question (Helbig, 2018). For example, when starting a research sampling topic, one can use the diabetic medication adherence in a 50-60-year-old males. Another example would be testing the pediatric population by studying the unimmunized patients versus the ones that were immunized and how they compare to the amount of times they were sick. This selects a population concerning a topic and will define what the sampling theory will be researching about. Generalizability is just another extension to sampling, where one goes the extra mile on conclusions of a result or how far went into researching the sample population or which population was chosen. Generalizability will be used a lot in the nursing research to see how in depth one went into the sampling theory or other types of theories for that matter.
Helbig, J. (2018). History and process of nursing research, evidence-based nursing practice, and quantitative and qualitative research process. In Nursing research: Understanding methods for best practice. Retrieved from: https://lc.gcumedia.com/nrs433v/nursing-research-understanding-methods-for-best-practice/v1.1/#/chapter/1