The false-alarm probability, a, and the power of process control charts depend on their control limits, which, in turn, depend on process parameters estimates. Process capability analyses also depend on those estimates. This dissertation initially presents a review - to our knowledge, the first in Portuguese - of the main research articles about the effect upon a of the estimation errors of the process parameters. All the works reviewed aim to determine, based on the probability distribution of the process parameters estimates (which is a function of the number of initial samples, m, and of their size, n), the expected value of a, or, equivalently, the expected value of the marginal distribution of the number of samples until a false alarm occurs. Our approach is different: to get (parameterized by m and n) the distribution of - and their percentiles or, equivalently, the distribution of the expected number of samples until a false alarm, in order to provide guidance on the initial number of samples to be used before setting the chart definitive control limits. The analysis was conducted for the S chart. The influence of the estimation errors on the power of the S chart was also examined. Finally, the distribution function was obtained, parameterized by m and n, of the estimation errors of the process capability index Cp, to provide guidance on the initial number of samples required to ensure, with a specified confidence level, a specified accuracy of the estimate.