Industrial Statistics with Minitab

10.1 Comparison of Two Means

10.1.1 Case 1: Independent Samples

Stat > Basic Statistics > 2-Sample t

Example 10.1:

Prat et al. (2004), in Métodos Estadísticos. Control y mejora de la calidad (Ediciones UPC, 2004), present a case study dealing with the comparison of two products (A and B) that are used in a leather tanning process. Ten pieces of leather are tanned using product A, another 10 with B. Once all 20 pieces are tanned the tensile strength of each piece is measured, obtaining the following data (in units of the measuring instrument):

Can we affirm that both products give different results with respect to the tensile strength?

Place the values of samples A and B in columns C1 and C2, respectively. Then, go to: Stat > Basic Statistics > 2-Sample t

Depending on how the data is organized, choose one of the three following options:

• Samples in one column: Choose this option when all data are contained in a single column (Samples) and another column (Subscripts) is used to indicate the corresponding treatment (for that, numeric codes like 1 or 2 may be used).
• Samples in different columns: Use this option when the values of each sample are contained in different columns. In our case, this option is chosen since we have placed the values of samples A and B in columns C1 ...