Class 3:  Births and Gender


Part 1:  Family planning

Suppose that a certain society values sons more than daughters. In this society, a couple will continue bearing children until they produce a son, at which point they will retire from the child-bearing business.

  1. Would this family-planning scheme tend to produce more boys, or more girls?
  2. Using coin tosses, simulate the generation of twenty families. Make histograms for the number of sons and the number of daughters. Find the percentage of boy babies and girl babies in your simulation. In light of this data, are you inclined to change your answer to the previous question?


Part 2: Gender bias in births

Read the first part of the article “U.S. Births Hint at Bias for Boys in Some Asians”. 

The article states, “In general, more boys than girls are born in the United States, by a ratio of 1.05 to 1.  But among American families of Chinese, Korean, and Indian descent, the likelihood of having a boy increased to 1.17 to 1 if the first child was a girl … if the first two children were girls, the ratio for a third child was 1.51 to 1 … in favor of boys.” 


1.     What does it mean that the ratio of boys to girls for the third child was 1.51 to 1 in favor of boys, when the first to children were girls?

2.     Suppose you flip a coin and it lands heads twice in a row.  If you flip it a third time, what is the chance that it lands heads again?

3.     Why do you think that the ratio for the third child is 1.51 to 1 and not 1 to 1 or 1.05 to 1? 

4.     The article goes on to say that “ … in China … the government’s one-child policy has resulted in the world’s highest sex disparity among newborns – about 120 boys born for every 100 girls”, and “In China, sex selection is usually achieved by aborting female fetuses.”  Estimate the fraction or percent of female fetuses that are aborted in China.


Journal Assignment:

Finish reading the article “U.S. Births Hint at Bias for Boys in Some Asians” and comment.

1) If couples could magically determine the sex of their offspring, what would happen? Would there be a sudden increase in the number of boys, or girls? If so, would this imbalance correct itself?

2) If society were able to prevent the use of this magical method, would it have the right to do so? If so, would it be well-advised to do so?



Homework Assignment 3 for Tuesday, Sept. 8: 

Do review exercises 2,4,7,10 in Ch 3.  Read Ch 4 and do review exercise 1, 3 in Ch 4.

By Sunday, complete and submit the questionnaire posted on Blackboard.