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Sample size calculator


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Estimate Sample size
Sample size for two samples A pilot study found that the dissociation constant (Kd) for ligand A and B are 9.5 +/- 1.2 nM and 5.7 +/- 1.5 nM. How many samples do we need to show KdA - KdB > 3 nM at the 95% confidence level? We may use the estimator for testing m1 - m1 = D (one-sided, independent). Reasonable estimates of parameters are a = 0.05 (95% CI), b = 0.1, D = 3, s = 1.5. Required sample size will be 5, i.e., the binding assays should be repeated at least 5 times.
For paired two samples, the differences should be calculated first, then treated as a one sample problem, i.e., testing for m (difference) = D.
Sample size for one sample In a microarray experiment, we would like to find out how many duplicate arrays needed for reliably claiming a gene's transcription is at least 2-fold up/down compared to the control. Suppose we are using cDNA arrays and the data is in the log-scale (log2R/G). Using the estimator for testing m = D (two-sided) and the following parameters: a = 0.01 (99% CI), b = 0.1, D = log22 = 1, s = log21.5 = 0.4 (1.5 fold up/down), we find the required sample size is 3.
Sample size for confidence interval A research would like to determine a mutant fruit fly's lifetime to the accuracy of +/- 5 days. On average flies live for 70 +/- 10 days. Using the sample size estimator for confidence intervals, he finds that he needs to measure the lifetime for at least 16 individual fruit files (a = 0.05, E = 5, s = 10).
Sample size for Pearson correlation A researcher has found that gene A's activity is proportional to gene B's activity (ya ~ k yb ). To quantitate the effect she would like to determine the ratio to the relative accuracy of +/- 20%. Note k is proportional to the Pearson correlation r and the relative error in k is equivalent to the absolute error E in r. She used sample size estimator for Pearson correlation and found at 95% CI (a = 0.05), the required sample size is 68.

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