Sample size: from formulae to concepts.

Sample size can be calculated from many online calculators or tables. But the use of these instruments is rational only when we understand our input data and the concept behind them completely. Terminologies like confidence interval, confidence limit, standard error of mean, margin of error, standard normal variate, power, significance level etc. and extent to which population size or chances of occurrence of an outcome can affect our sample size remain to be well understood before using these software solutions.