Used when we want to estimate what is the mean of some characteristic in the population based on the data collected in the sample. eg we want to know the average value of the tensile strength of the metallic alloy X, being that we made 10 specimens and found for this sample an average of 50 kgf/mm2 and a standard deviation of 5 kgfmm2. This is the average resistance in the sample, but what would be the average in the population of specimens? The result will be something like IC 95% = 46.4 to 53.6 kgf/mm2. This means that the estimate for the population is between 46.4 and 53.6 kgf/mm2.