I propose to determine factors influencing bacteriological and clinical cure in dairy cows with clinical mastitis after treatment with antibiotics. I propose to follow clinically healthy (i.e. without clinical mastitis) lactating cows for the development of new clinical mastitis and also for cure (Bacteriological and clinical cure) of the affected animals after treatment. But there is no any comparison group, i.e. no control group or treatment group (as the antibiotics are also factors to be studied with respective to their type, dosage and others). In addition with this, it is new to be conducted in my country (Ethiopia) which is seems to me difficult to take the previous proportions conducted in developed countries as a proportion estimate in my study due to management or other facilities difference. So my questions are:
1. How do I determine the sample size?
2. Could I use the 50% proportion as proportion estimate in this case?
https://www.qualtrics.com/blog/calculating-sample-size/
find online sample size calculator
Berhe Mengistu your study seems partial epidemiology and partial experimental type. Remember you may want to choose simple random sampling for your epidemiology estimated with help of your local prevalence rate of mastitis by given formulas in Thursfield's book for epidemiology. As for your experimental work, whatever experimental design you may choose, you should have minimum six replicates of each treatment.
Good luck
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