Class 19: Sperm Count


Read the Time Magazine article "What's wrong with our sperm?" and the NY Times article "Sperm counts: some experts see a fall, others see bad data".

What are some of the differences in the way the two articles address this topic? Which is better?

What are some of the problems of meta-analyisis (combining data from past and present studies) in order to decide whether sperm count is declining? What factors should you control for?

How would you design a study to test the hypothesis that sperm counts are declining?

The NY Times article cites Dr. Sherins that there is no evidence that infertility is on the rise in the United States. If this is so, why worry about sperm count?

If infertility is on the rise, what might be the reasons?

For next time

Read the articles "Declining sperm counts" and "Time series analysis of sperm concentration ..." from the British Medical Journal. Think about the following questions that we will discuss next time.

The section subtitled "Results" begins with the sentence "When the age of donors was examined with respect to the year of their first donation, there was no evidence that the age of donors had changed during the period of data collection." What do you think this means, and why do they mention it?

The next paragraph mentions that sperm concentration decreased by 2.1% per year, with similar decreases for total number of sperm and total number of motile sperm. Where do these figures come from? If the trend continues, when is Doomsday?

In Table 1, what are the numbers in parentheses? In Table 2, what do the P values mean?
How do you read the box plots in Figure 1?