Understanding Scientific Research

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Consumers Home > DES Research > Understanding DES Research > Understanding Scientific Research

Understanding Scientific Research

Understanding DES Research

	Overview

	Understanding Scientific Research

	Deciding Whether a Source is Reliable

	Role of Laboratory Animal Studies

	Role of DES Cohort Studies

Several journal article citations are provided in CDC's DES Update fact sheets. How do I read a citation?

Knowing how to read a citation for a journal article will help you find it either at the library or on a Web site. The following is an example citation for a journal article about DES:

Hatch EE, Palmer JR, Titus-Ernstoff L, Noller KL, Kaufman RH, et al. Cancer risk in women exposed to diethylstilbestrol in utero. JAMA 1998;280(7):630-4.

The authors who wrote the article are listed first. If there are several authors, only the first few authors' names will be listed, followed by "et al." The complete title comes next. The name of the journal where the study was published follows. Oftentimes, the name of the journal will be an acronym. For example, in this case, JAMA stands for Journal of the American Medical Association. The year the study was published is next. A new issue of this journal is printed each week, so the citation includes the volume (280) and issue number (7). The citation also includes the page numbers (630-4) of the article.

If you have difficulty reading a citation or finding an article, ask a librarian for help.

Where can I find copies of scientific journal articles?

Community libraries often have copies of well-known scientific journals. Hospital or university libraries may have a wider range and older issues of these journals. Some journals also have articles available on their Web sites. Some Web sites offer the articles free of charge, but others may require you to register with the site and pay a nominal fee. You will need the citation for the article to find it either at the library or on a Web site. See the answer to the previous question for an example citation.

What does it mean if an article or journal is "peer reviewed?"

Scientific journals require research articles to go through a process called "peer review." During peer review, scientific experts who were not connected to the study review the article and decide whether it was done properly and whether the findings have merit. Only studies that pass peer review get published.

What does it mean when researchers say that results are "statistically significant?"

Because health problems occur for a variety of reasons, including chance, researchers must determine if a health effect they are studying may have occurred in study participants as a result of chance alone. Specifically, "statistical significance" refers to a finding in a research study that is larger or smaller than would be expected by chance alone.

Statistical significance is expressed in scientific journals by a probability value (p-value). P-values are calculated using a statistical formula that includes the number of people and health effects being studied and is designed to answer the question, "Could a group of this many people, who all experienced a common exposure, have had this health problem in common by chance alone?" A finding is considered statistically significant if there is less than a 5% probability (p=.05 or less) that the findings resulted from chance. Conversely, if there is greater than a 5% probability (p=.06 or greater) that a finding resulted from chance, the finding is not statistically significant.

How do I interpret statistics in research about DES-related health risks?

Understanding research about DES-related health risks without knowing how to interpret statistics can be difficult. The following table offers some examples of how scientific studies present risk information.

Different Ways that Studies Describe Risks	Statistical Phrase	Risks Presented as Ratios	Risks Presented as Decimals or Percentages	Type of Risk
In the general population, a woman's lifetime risk of developing breast cancer is about one in eight. That means that, over a lifetime, in a group of eight women, one of those women would be expected to be diagnosed with breast cancer.	One in eight	1:8	.13 or 13%	Absolute risk*
For women prescribed DES while pregnant, lifetime risk of developing breast cancer is one in six. That means that, over a lifetime, in a group of six women exposed to DES during pregnancy, one of those women would be expected to be diagnosed with breast cancer.	One in six	1:6	.16 or 16%	Absolute risk
For women prescribed DES while pregnant, the risk for breast cancer is approximately 30% higher than for women who were not exposed to DES during pregnancy.	Approximately 30%	From 1:8 to 1:6	.30 or 30%	Relative risk**
Source of risk information in this chart: Titus-Ernstoff L, et al. Long term cancer risk in women given diethylstilbestrol (DES) during pregnancy. Br J Cancer 2001;84:126-33. The absolute risk is a number that represents the probability that an individual with a special risk factor (such as exposure to DES) will experience a health effect (e.g., breast cancer). * Relative risk is the comparison of disease rates (e.g., breast cancer) between persons with higher risks and those in the general population (who have no special exposure).

What is a "cohort" study?

A "cohort" is a group of people who share common characteristics or experiences. By compiling and summarizing data from a cohort, scientists can observe whether disease conditions develop at higher rates in a cohort group than they would expect in the general population.

In this case, a DES cohort is a group of people who were exposed to DES. Scientists have been following DES cohorts for several years, to evaluate their medical conditions and disease rates. Researchers are trying to determine whether DES-exposed women and men are at an increased risk for certain health problems compared with the general population. For instance, one cohort study revealed that one in six women prescribed DES while pregnant can be expected to develop breast cancer in her lifetime, compared with an expected rate of one in eight women in the general population (Titus-Ernstoff et al., 2001). Learn more about the DES Cohort Studies.