Week 6 - Reliability & Validity

Week 6 is about assessing the validity and reliability of diagnostic and screening tests. Validity and reliability, sensitivity and specificity, and positive predictive value and negative predictive value will be discussed.

Based on the passage below answer the questions that follow.

Diabetes is a disease in which the body does not produce or properly use insulin. Insulin is a hormone that is needed to convert sugar, starches, and other food into energy needed for daily life. The cause of diabetes continues to be a mystery, although both genetics and environmental factors such as obesity and lack of exercise appear to play roles.

Type 2 diabetes is the most common form of diabetes. In type 2 diabetes, either the body does not produce enough insulin or the cells ignore the insulin. Insulin is necessary for the body to be able to use sugar. Sugar is the basic fuel for the cells in the body, and insulin takes the sugar from the blood into the cells. When glucose builds up in the blood instead of going into cells, it can cause two problems:

• Right away, your cells may be starved for energy.
• Over time, high blood glucose levels may hurt your eyes, kidneys, nerves, or heart.

While diabetes occurs in people of all ages and races, some groups have a higher risk for developing type 2 diabetes than others. Type 2 diabetes is more common in African Americans, Latinos, Native Americans, and Asian Americans/Pacific Islanders, as well as the aged population.

In order to determine whether a patient has pre-diabetes or diabetes, healthcare providers conduct a Fasting Plasma Glucose Test (FPG) or an Oral Glucose Tolerance Test (OGTT). Either test can be used to diagnose pre-diabetes or diabetes. The American Diabetes Association recommends the FPG because it is easier, faster, and less expensive to perform.

With the FPG test, a fasting blood glucose level between 100 and 125 mg/dl signals pre-diabetes. A person with a fasting blood glucose level of 126 mg/dl or higher has diabetes.In the OGTT test, a person's blood glucose level is measured after a fast and two hours after drinking a glucose-rich beverage. If the two-hour blood glucose level is between 140 and 199 mg/dl, the person tested has pre-diabetes. If the two-hour blood glucose level is at 200 mg/dl or higher, the person tested has diabetes. Assume that the laboratory cost for performing a FPG costs $26 per test and the OGTT costs $46 per test.

The state legislature in your state is considering a bill to make screening for diabetes a mandatory (and reimbursed) component of health check-ups of adults, aged 20 and older. The governor wants to assemble a team of experts to evaluate the scientific evidence base, the benefits, and costs of this proposal. The governor turns to you, the State Health Director, for advice on proceeding with this evaluation.

1. What sources for estimating the likely prevalence of diabetes in the population of your state may be available and what limitations might they have?
2. How will diabetes prevalence effect testing results?
3. The American Diabetes Association requires that an initial positive test must be confirmed, on a subsequent day, by measurement of either fasting plasma glucose, a two-hour plasma glucose, which is part of an oral glucose tolerance test (OGTT), or a random plasma glucose test if symptoms are present. Explain to the governor why a second test must be used as a confirmatory test for asymptomatic persons who initially screen positive?
4. Assume your state has a population of 2,894,000 over the age of 20 in 2001 and assume that 10% of adults will come in contact with a healthcare provider on an annual basis. Based on the total projected cost of diabetes testing in your state over the year (you can calculate this!), are these data sufficient for you to make a recommendation to the governor regarding the proposed legislative bill?

**Make sure to address all parts of the assignment.***

Student Objectives for the Week:

• Define validity and reliability
• Describe the requirements of screening programs
• Differentiate between the sensitivity and specificity of screening tests
• Differentiate between positive predictive value and negative predictive value
• Describe the Kappa Statistic

Read PDF : Week 6 HW