The Obstacle Course

Man Jumping a Hurdle

Questions to test your understanding

Thinking man icon with question below

When investigators gathered data on the number of motor vehicles in use over time, they found that the increase correlated strongly with the increase in lung cancer mortality. The correlation is evidence of an association between motor vehicle use and lung cancer mortality. Does this indicate that motor vehicle use is a cause of lung cancer mortality?

a. Yes, because there was a "strong" correlation, indicating a strong association.

b. No, because the data on the number of motor vehicles being used was probably grossly inaccurate.

c. No, because the sample size is unknown.

d. No, because these data are from an ecological study, and it is dangerous to conclude that there is a causal relationship from these studies because of the ecological fallacy and the inability to control for many possible confounding factors.

Thinking man icon with questions below

A sample of 100 middle aged and elderly women was followed prospectively for 10 years in order to study rates of ovarian cancer. All subjects entered the study on January 1, 1990, and all were free of cancer at the beginning. All women were followed until December 31, 1999. None were lost to follow-up. During this period, five subjects were diagnosed with ovarian cancer, but they all survived to the end of the study.

Case #1 was diagnosed with ovarian cancer in January 1991.

Case #2 was diagnosed in January 1992.

Case #3 was diagnosed in January 1993.

Case #4 was diagnosed in January 1986.

Case #5 was diagnosed in January 1996.

The time at which these 5 subjects developed cancer is shown in this table:

Use this information and the information in the table below to answer the questions beneath the tabl:

Subject	1991	1992	1993	1996	1998
Case #1	cancer
Case #2		cancer
Case #3			cancer
Case #4				cancer
Case #5					cancer

Thinking man icon. There are 6 questions to answer below the table and other information

Use this information and the information in the table below to answer the questions beneath the table:

In January of 1990, 1,010 young adults offered to participate in a 10-year prospective study to determine their risk of Type-I diabetes. This group underwent an initial blood test to determine whether they were diabetic, and eligible subjects were re-tested yearly for the next 10 years. Among the group that offered to join the study:

There were 2 individuals who were found to have diabetes on the initial blood screening; these 2 people were referred for treatment and were not enrolled in the study
There were 1,000 who were disease-free and remained disease-free for the entire 10 years of the study
6 individuals developed diabetes during the course of the study at the times indicated in the table below
2 individuals who were initially disease-free were lost to follow-up during the study at the times indicated in the table below

? = Lost to follow-up + = Blood test positive for diabetes ------ = Continued disease-free follow-up

Subject #	1990	1991	1992	1993	1994	1995	1996	1997	1998	1999
1	------	------	+
2	------	------	------	------	------	------	------	------	------	+
3	------	------	------	------	------	------	------	+
4	------	+
5	------	------	------	------	+
6	------	------	+
7	------	------	------	------	?
8	------	------	------	------	------	?

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