Today

• Today: Review

• Assignment Due Wednesday in the Statistics Main Office:– 12.5, 12.9, 12.13a, 12.19 (use t-test)

Example

• In recent years, there has been growing concern about the health effects of video display terminals (VDTs)

• It is known that the miscarriage rate of a pregnancy under normal conditions is about 20%

• In a survey of 150 part-time female employees who used VDTs at least 20 hours per week, there were 50 reported miscarriages

• At the 1% significance level, is there evidence that exposure to VDTs is increasing the miscarriage rate

Example (Pulp Mill)

• An important measure of performance at pulp mills is based on pulp brightness measured by a reflectance meter

• An investigation was performed (Sheldon, 1960; Industrial and Engineering Chemistry ) to investigate if there is a difference in product quality for different mill operators

• Want to see if there are differences in the reflectance for 2 different operators

• Data:

Operator A B

59.8 59.8 60.0 60.2 60.8 60.4 60.8 59.9 59.8 60.0

• Is there evidence at the 0.10 level that the operators perform differently?

• Assumptions:

Example (Call Center)

• A company wishes to monitor customer service

• A senior manager claim that the average waiting time is 3 minutes

• Customers have been complaining that the waiting time is more than 3 minutes

• The waiting times of 75 randomly selected calls to a customer service hot-line were recorded

• The calls had a sample mean of 3.9 minutes and sample standard deviation of 2.4 minutes

• Test this claim with a significance level of 0.05

Example (Calcium Intake)

• The recommended daily allowance (RDA) of calcium for women between the ages of 18-24 years old is 1200 mg

• It is felt that women are not getting the required amount

• A study was performed to see if women were getting the RDA

• A sample of 20 women in the desired age group were sampled and their daily calcium intake was estimated

• The sample mean and standard deviation 930.02 and 427.23 respectively

• Is this evidence that women get less than the recommended daily allowance?

Example (Opinion)

• Even though Puerto Rico is a territory of the United States, there are many cultural differences between the States and the island of Puerto Rico. These differences may include the way in which consumers handle problems with purchases.

• A manufacturing company decided to conduct a survey of their customers to see if there the customer's location impacted whether they would complain if there was a problem.

• The people who experienced a problem with their purchase were asked if that had complained.

Example (Opinion)

• The results are summarized below

Complained Continental United States Puerto Rico No 94 33 Yes 330 64