Expert: Sherry Wallin - 10/12/2011

Question
Hi there, I was trying to understand the following portion of an article, which stated:

A) "... the probabilities increased towards a peak of 0.37 occurring 2 days prior to ovulation and decreased thereafter.

and

B) "The peak probability varied from 0.05 for a couple in the 5th percentile of the population distribution to 0.83 for a couple in the 95th percentile."

I'm having difficulties understanding the meaning of paragraph A vs. paragraph B. I can copy and paste the graph to you, but it reflects the above wording.

I'm interpreting paragraph A to mean that there is a 37% chance of pregnancy two days before ovulation which is the peak probability, but I don't know what the author is referring to in paragraph B. eg. the peak probability being compared to percentiles.

How do the two charts relate to each other is in essence my query.

Thanks,

Answer
J~

Your interpretation of the first graph is accurate except the probability approached a maximum of 37% 2 days prior to ovulation and made an abrupt turn and went toward 0 again on that 2nd day prior to ovulation as well.

The 2nd paragraph is saying that for an couple in the 5th percentile (which means if you lined up 100 couples there were 95 couples in front or above the couple in the 5th place) has a max probability of 5% whereas the couple in 95th place had a max probability of 83%. This graph has a possibility of the samples being from different populations.

Ultimately these two graphs have very little to do with each other, other than they appear to be about couples and ovulation.

Math Prof