The 2-Sample t conducts a hypothesis test of the difference between two population means when the population standard deviation, s is unknown. It also calculates a confidence interval of the mean. This procedure is based on the t-distribution which is derived from a normal distribution. The samples should be drawn independently from each other. For dependent samples, use the Paired t-test.
| Test | Null Hypothesis, H0 | Alternate Hypothesis, H1 |
| One-tailed | m1 - m2 = d | m1 - m2 = d or m1 - m2 > d |
| Two-tailed | m1 - m2 = d | m1 - m2 <> d |
where m1 and m2 are the population means and d is the hypothesised difference between the population means.
At the Excel Menu (For Excel 2007, go to Add-ins first)
Choose ProcessMA > Statistics > Basic Statistics > 2-Sample t
For data in different columns
In Variable 1, select the column containing the data for the first sample (Numeric)
In Variable 2, select the column containing the data for the second sample (Numeric)
For data in single stacked column
In Variable, select the column containing the data for both samples (Numeric)
In Subgroup, select the column containing the subgroup indicator (Exactly 2 distinct values)
In Test Mean Difference, enter hypothesized difference between the population means (Numeric)
In Alternate, select the appropriate alternate test
In Confidence Level, enter value for confidence level (Numeric, >0 & <1)
Check Assume Equal Variances, if you want to assume that both populations have equal variances
Click OK
A tire manufacturer wants to compare the wear and tear of 2 types of new tires, A and B. Ten motorcycles were fitted with Tire A and another ten motocycles were fitted with Tire B. After 6 months, the amount of wear and tire on the tires were measured.
Open data worksheet by choosing ProcessMA > Tools > Data
Choose ProcessMA > Statistics > Basic Statistics > 2-Sample t
In Variable 1, select BL - Tire-A
In Variable 2, select BM - Tire-B
Click OK
For a desired a = 0.05, since p = 0.6491 > a, we fail to reject H0. Therefore, we conclude that there is no significant evidence that the wear and tear of the two types of new tires are different.
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