Dear experts,
Well its known that the higher the sample size, the more the financial expenditure. Will the 30 sample size justifies the cost of operation and the data to be valid?
although there is not clear about waste, but 30 samples are adequate for valid data.
Well my take is usually a higher sample size enhances the generalization ability. However, other constraints such as finances, accessibility to the sample and geographical location of the sampling region could lead to a lower sample size. This however requires adequate justification. I believe your no. 30 could be adequate if justified and based on the study site size, which is not specified. My advice do adequate justification and you are good to go.
Joan Nyika gives very good advice. The 30 is a magic number that was once believed to allow you to use the normal approximation to the t-test, etc. That is now debunked. How ever as an experieced water lab technician I think that 30 may be a good choice. With that I would follow Joan's advice and also look at books like this: https://b-ok.cc/s/Water%20and%20waste%20water%20analysis .
Best wishes, David Booth
Dear Joan Nyika when you say adequate justification, would be enough if there are published literature which have done the same? but how about if the population is about 100,000?
Well Marcelino Lunag Jr if it is a population of 100,000 of course chances are representation cannot be realized unless you use some equations that are found in literature to narrow down the population to that number. That is what I mean by justification. Otherwise, one would tend to question why 30? why not 10? why not 100?
Thanks very much for your answers Joan Nyika and David Eugene Booth
Marcelino Lunag Jr Remember the length of a confidence interval depends on
sigma/sqrt(n) not the population N for sample size large but still much less than 100,000 Big populations don't need very large n just because they are bigger. see this link: https://b-ok.cc/book/2324520/acf6e2
Best, David Booth
Dear Marcellino,
it also depends on type of waste, e.g. liquid, solid, etc. Let me explain better.
The sampling standard UNI 10802 and EN 14899 provide, if we do not have adequate information about the composition of the waste such as to allow the definition of a sampling plan, to provide for a preliminary investigation in order to acquire the initial basic information on the waste.
Wastes have usually high heterogeneity due to seasonality, place, etc., and heterogeneity has to be considered in the sampling plan.
If liquid waste, it is easier to mix it and get less heterogeneity.
Good luck, especially if solid waste.
http://store.uni.com/catalogo/index.php/catalog/product/view/id/47944/s/uni-en-14899-2006/category/48/?___store=en&josso_back_to=http%3A%2F%2Fstore.uni.com%2Fjosso-security-check.php&josso_cmd=login_optional&josso_partnerapp_host=store.uni.com&___from_store=it
http://store.uni.com/catalogo/uni-en-16192-2012
http://store.uni.com/catalogo/uni-10802-2013?josso_back_to=http://store.uni.com/josso-security-check.php&josso_cmd=login_optional&josso_partnerapp_host=store.uni.com#
Dear Roberto Molteni sir,
I agree sir that type of waste, its seasonal variation, heterogeneity and study site are important considerations. Thank you very much for the links above which is of big help. But will this pandemic and our current situation affects greatly the waste generation? is it advisable to conduct waste analysis?
This pandemic and our current situation affect greatly the waste generation, at least for countries in lockdown.
Regarding your question, “is it advisable to conduct waste analysis?”, depends on your research goal. If you want to assess the “normal” waste production, of course the it is not advisable.
although there is not clear about waste, but 30 samples are adequate for valid data.
Welcome Marcelino Lunag Jr ,
if your research is on composting, I would like mention the Italian experience: https://www.compost.it/en/
Sir Aijaz Panhwar thank you much for your response and Sir Roberto Molteni this website will be a great help for me. I am currently on biowaste analysis and composting.
Sample size of 30 is not a law, its for convenience for triking a moderation between cost and accuracy
I think that the high number of samples, although important, but it is not necessarily significant in the case of waste analysis. The frequency and periodicity of sampling are decisive during analysis.
Dear Mohamadou Adamou what would be the minimum frequency or period is valid in general.. is it alright for a three-day analysis or seven-days or 1-month analysis? or it depends on local manual and guidelines?
Regarding the sampling frequency, have a look:
https://www.google.com/search?ei=TMbLXv6nHbCajLsP6o6b6Ao&q=frequency+sampling+of+solid+waste+&oq=frequency+sampling+of+solid+waste+&gs_lcp=CgZwc3ktYWIQAzoFCCEQoAE6BggAEBYQHjoECCEQClCOzwNYsu8DYKuEBGgAcAB4AIABiwKIAbsGkgEFMS4wLjOYAQCgAQGgAQKqAQdnd3Mtd2l6&sclient=psy-ab&ved=0ahUKEwj-_bHUjc_pAhUwDWMBHWrHBq0Q4dUDCAs&uact=5
Local manual and guideline are usually less useful because need complying with laws (not science).
The typology and characteristics of waste depend on human activities and since waste is continuously degraded after it is produced, it is important to collect it immediately after collection, which takes place during a period of the day either in the morning or in the evening depending on the location, taking into account the frequency of collection during the week (e.g. every day or every two days). The duration of the analyses depends mainly on the financial means and the objectives that are set.
Seasons during the year can influence the initial composition of the waste. Therefore, these are important aspects to take into account if you want to carry out a waste characterisation.
It is essential to use local manuals and guidelines to comply with the relevant laws and regulations if they exist.
Sample size is a matter of cost, time and accuracy. The higher the sample size the better. But along with sample size, you should take care to do the sampling on different time conditions e.g different hours of a day, different days of the week, different months and different seasons. That's the way you would have a trustworthy and representative sample.
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