Reference no: EM133463401

Many people in the United States and Europe use hair dyes. It is estimated that more than one-third of women over age 18 and about 10 percent of men over age 40 use some type of hair dye. Over 5,000 different chemicals are used in hair dye products. Early hair dye formulations contained chemicals, including aromatic amines, that were found to cause cancer in animals. In the mid- to late 1970s, however, manufacturers changed the components in dye products to eliminate some of these. It is not known whether some of the chemicals still used in hair dyes can cause cancer. Given the widespread use of hair dye products, even a small increase in risk may have a considerable public health impact, so scientists have tried to determine if there is an association with human cancer.

Over the years, some population studies have found an increased risk of bladder cancer in hairdressers and barbers. In addition, studies have linked the personal use of hair dyes with increased risks of certain cancers of the blood and bone marrow, such as non-Hodgkins lymphoma (NHL) and leukemia, but other studies have not shown such links. Studies of breast and bladder cancer have also produced conflicting results. Relatively few studies have been published about the association of hair dye use with the risk of other cancers. Based on its review of the evidence, IARC concluded that personal use of hair dyes is "not classifiable as to its carcinogenicity to humans". [Source: National Cancer Institute]

Case study

Questions

You are an epidemiologist studying use of hair coloring as a risk factor for two specific cancer outcomes: NHL and bladder cancer. You decide to approach the Centers for Disease Control & Prevention (CDC) for support to conduct your study.

1. What kinds of epidemiologic information would you provide to the CDC to justify your request for money to study cancer outcomes related to hair dye? Where would you get this information? Describe sources specifically, and explain why you feel these would be the best sources.

2. You review the existing literature, and are given the okay to go ahead by CDC. Now, what kind of study would you plan to do? State clearly the overall design, your strategy for choosing participants, and how you will specify risk factors and outcomes. State the null and alternative hypotheses for your study. Why did you choose this particular approach?

3. What are the major biases you'd expect to encounter in carrying out your study? How would you set up your study to minimize the impact of these potential biases? What impact could these biases have on the validity and results of your study?

4. You complete your study and report that indeed, there appears to be an association of NHL with prior history of long-term use of hair coloring. The association is statistically significant at the 95% level. What additional information might increase your belief that this is a true effect, rather than an artifact?