the correlation coefficient

 T-test (1 of 2)

Difference testing is used primarily to identify if there is a detectable difference between products, services, people, or situations. These tests are often conducted in business situations to:

· Ensure a change in formulation or production introduces no significant change in the end product or service.

· Substantiate a claim of a new or improved product or service

· Confirm that a new ingredient/supplier does not affect the perceived attributes of the product or service.

· Track changes during shelf life of a product or the length of time of a service.

Differences Between Two Independent Sample Means:

Coke vs. Pepsi. Independent sample t-tests are used to compare the means of two independently sampled groups (ex., do those drinking Coke differ on a performance variable, or the numbers of cans consumed in one week) compared to those drinking Pepsi. The individuals are randomly assigned to the Coke and Pepsi groups. With a confidence interval of ≤.05 (corresponding probability level of 95%) the researcher concludes the two groups are significantly different in their means (average consumption rate of Coke and Pepsi over a one week period of time) if the t-test value meets or exceeds the required critical value. If the tvalue does not meet the critical t value required then the research investigator simply concludes that no differences exist. Further explanation is not required. Presented below is a more useable situation.

 T-test (2 of 2)

Differences Between Two Means of Correlated Samples

Correlated t-test statistical processes are used to determine whether or not there is a relationship of a particular measurement variable on a pre- and post-test basis. Oftentimes when there exists a statistically significant relationship on a pre- and post-test basis the business manager can use the first measurement values to predict the second in future situations without having to present a post-test situation.

Example: Using the same data presented above let us assume that there are not two independent groups but the same group under two different conditions—noise production environment and non-noise production environment.

Using the raw data and formula above to calculate the t-test value the actual t-test, when calculated properly, is 3.087. By going to the appropriate t tables in your text book find the critical value for t at the .05 confidence interval. The value you should find is 1.895.

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