I want to see prevalence of PE and ED in patients with thyroid derangement. I found in one study, in case of hyperthyroidism, prevalence of PE and ED is 50% and 14.7% respectively and in case of Hypothyroidism, prevalence of PE and ED (along with HSD and DE) is 7.1% and 64.3% respectively. They worked with only 48 patients. their study design was prospective study as they followed up the same patients once.
my study is cross sectional. As it is for thesis purpose , a small sample will be convenient for me. Please suggest me.
Thanks in advance...
The attached shows how to calculate sample size in order to estimate prevalence with required precision
If you are interested in power studies for significance of differences in proportions, the attached gives methods.
To estimate a prevalence (P), the sample size is: n = z²PQ/u². With Q= 1-P, u = required precision, z = 1.96 for α = 5% . If several estimates of P are advanced, the one that generates the largest sample size is selected. At the same required precision and α error , the estimated sample size is the greater the closer P is to 50%. If we have no idea of P, we can adopt the most unfavourable situation where P = Q = 0.50. Hence: n = z²/4u². For example, for an required precision of 0.020 (2.0%), at risk 5%, the sample size to be taken is: n = 1.96² / (4 * 0.02²) = 2401.
To avoid all these calculations use the free OpenEpi calculator :
Sample Size for % Frequency in a Population (Random Sample)
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