Excel’s TINV function (CONFIDENCE.T) is what the quality engineers at Rolls Royce would use to compute the confidence interval (confidence.t). This function calculates the inverse of the Student’s t-distribution, which is frequently used in hypothesis testing and determination of confidence intervals when the sample size is small and the population standard deviation is unknown. The TINV function requires two arguments: the confidence level (e.g., 0.05 for a 95% confidence interval) and the degrees of freedom, which are equal to the sample size minus 1.
The CONFIDENCE.NORM function computes the confidence interval for a population mean based on the normal distribution, given that the population standard deviation is known. Due to the fact that the population standard deviation is generally unknown in practise, this function would not be the best choice in this situation.
