Hi Pablo,

I'm not sure that there are too many debates between qualitative and quantitative sampling design and techniques. Essentially, one is usually non-probability sampling and the other probability. It depends if you are coming from a particular paradigm stance as to whether one thinks there are threats. For instance, if one is a positivist researcher - they may think that qualitative sampling lacks certain types of control or rigour whereas post-positivist might argue the opposite that there is not enough flexibility with probability sampling. At the end of the day, the argument is mute. No one technique is better than another. It's about purpose and fitness for task. Therefore, I don't personally see it as benefits and threats. All sampling techniques need to be properly applied and due rigour attended to - then there are no threats. 

The first part of the attached chapter may assist. 

Thanks very much for sharing this helpful chapter Dean.  

Thanks Dean, can you give the name of the book that contain the chapter you attached. For citation.

Hi Kim - no problem!!

Pablo - below is pasted the source for the chapter. It is in the 2013 4th edition. However, the 5th edition came out in 2016 (which is updated) - but I cannot upload the proofs for that edition. 

I hope that helps.

Best,

Dean

Schneider Z, Whitehead D, LoBiondo-Wood G & Haber J (2013) Nursing & Midwifery Research: Methods and Appraisal for Evidence-Based Practice. 4th edn. Elsevier - Mosby, Marrickville, Sydney.

Schneider Z, Whitehead D, LoBiondo-Wood G & Haber J (2016) Nursing & Midwifery Research: Methods and Appraisal for Evidence-Based Practice. 5th edn. Elsevier - Mosby, Marrickville, Sydney.

Dear Pablo

The only issue is chance factor and whole representation of population. However with qualitative sampling also you will get the result which may not be same while repetitive experimentation. 

Yes, one can not say with certainty about the result obtained from the probability sampling.

So, personally I feel using qualitative sampling is not a big problem if it is being used judiciously.

Regards

Just as qualitative and quantitative research typically serve different purposes, qualitative and quantitative sampling also meet different goals. For qualitative research, this means using smaller, purposive samples to target specific issues in specific sets of participants. In quantitative sampling, this means seeking representativeness and generaliazability to make connections to larger populations.

The following papers should be helpful, particularly the strengths and weaknesses of quantitative and qualitative research, namely: Libarkin and Kurdziel (2002, pp. 78-79); Johnson and Onwuegbuzie (2004, pp. 19-20). 

• Gelo, O., Braakmann, D. and Benetka, G. (2008). Quantitative and Qualitative Research: Beyond the Debate. Integrative Psychological and Behavioral Science, 42, 3, pp. 266-290.
• Johnson, R. B. and Onwuegbuzie, A. J. (2004). Mixed Methods Research: A Research Paradigm Whose Time Has Come. Educational Researcher, 33, 7, pp. 14-26.
• Libarkin, J. C. and Kurdziel, J. P. (2002). Research Methodologies in Science Education: The Qualitative-Quantitative Debate. Journal of Geoscience Education, 50, 1, pp. 78-86. 

Benefit: You will have opportunity to understand in detail about the context in which study events occur. 

Disadvantage: Limited data source i.e respondents implying diversity may lack

I don't think there are any actual 'threats' lol. I think you may have meant 'disadvantages'? Anyway, apart from probability and non-probability testing (as Dean mentioned), there is also Bayesian testing, a method of statistical inference in which Bayes' theorem is used to update the probability for a hypothesis as more evidence or information becomes available. And also, techniques such AIC, a measure of the relative quality of statistical models for a given set of data.These methods are probably intermediate between quali and quanti. Tative, that is lol :)

According to Interaction, strengths and weaknesses of quantitative evaluation designs are. among others, the following:

Strengths

1-Study findings can be generalized to the population about which information is required.

2-Samples of individuals, communities, or organizations can be selected to ensure that the results will be representative of the population studied.

3-Structural factors that determine how inequalities (such as gender inequalities) are produced can be analyzed.

4-QUANT estimates can be obtained of the magnitude and distribution of impacts.

5- QUANT estimates can be obtained of the costs and benefits of interventions.

6- Clear documentation can be provided regarding the content and application of the survey instruments so that other researchers can assess the validity of the findings.

7-Standardized approaches permit the study to be replicated in different areas or over time with the production of comparable findings.

8- It is possible to control for the effects of extraneous variables that might result in misleading interpretations of causality (although this can be challenging in the natural settings of evaluations).

Weaknesses

1-Many kinds of information are difficult to obtain through structured data collection instruments, particularly on sensitive topics such as domestic violence or income.

2- Many groups such as sex workers, drug users, illegal immigrants, squatters and ethnic minorities are always difficult to reach, but the problems are often greater for QUANT data collection methods.

3- Self-reported information obtained from questionnaires may be inaccurate or incomplete.

4-There is often no information on contextual factors to help interpret the results or to explain variations in behavior between households with similar economic and demographic characteristics.

5-The administration of a structured questionnaire creates an unnatural situation that may alienate respondents.

6-Studies are expensive and time-consuming, and even the preliminary results are usually not available for a long period of time.

7-Research methods are inflexible because the instruments cannot be modified once the study begins.

8-Reduction of data to numbers results in lost information.

9-The correlations produced (e.g., between costs and benefits, gender, and access to services or benefits) may mask or ignore underlying causes or realities.

10-Untested variables may account for program impacts.

11-Errors in the hypotheses tested may yield misimpressions of program quality or influential factors.

12-Errors in the selection of procedures for determining statistical significance can result in erroneous findings regarding impact.

What are the main benefits and threats of qualitative sampling design?

Personally I don't think there is any threat to qualitative sampling design because this type of design as part of research method is dependent on research problem, research objectives, research questions or even the conceptual framework / research model.  Quantity of the sample in a qualitative research is dependent on the research objective whether it is deep dive into specific phenomenon discovery whereby single sample is good enough or multiple samples until saturation of data collection is reached.

One of the challenges of qualitative research is bias in interpretation of teserch result

Thanks to all that have written an answer to my question, they will be very useful for my predoctoral exam 

The purposes of quant and qual are different. qual is to understand why, the lived experience. sampling depends on your research question, the problem you are investigating and your objectives. So sampling is often purposeful in qual, but driven. Y carefully thought through criteria