The curious case of gender imbalance in Hong Kong
This chart is from an old post in Simonworld (where are you now Simon?).
It does not need much explanation. In 1990 There were more male than female across all age groups (till around 60 when men begin to die a lot faster). By 2005 (15 years later) the females outnumbered males VERY significantly.
For more critical minds, one cannot help but ask the question, how could there be so large a change in such a short time span? We are talking about a change from -7% to +33% in the 35-39 age group! i.e. in 1990 there are 107 men for every 100 women, 15 years later, it is 67 vs 100.
It must not be a result of "natural process". In fact, the female:male ratio at birth has been at a fairly stable 49:51 throughout the 1960s, and grew to 48:52 by 1980s and stabilized through this date (i suspect a small amount of selective abortion led to this rise), according to HK Government Census (you need to download excel format to see all the yearly data).
Another evidence that this is a "non-natural" process is revealed by the 35-39 cohort data in 2005, who were 20-24 in 1990, for every 100 men there were 96 women in 1990 but 133 in 2005! Where did these 37 people come from?
Well, it must be non-natural, which is immigration - emigration - death.
Death rate is small for younger age (typically under 1% as we can safely assume). Since one does not need to give up the residency in Hong Kong, emigration has no impact on HK ID card holder (but I am not exactly sure about this, which depends on the definition of the census). The reason must be deal to NET immigration.
How could this happen? Well, the most likely cause is, HK men married women from outside HK (mainly from mainland China). Therefore, if you read from news that it is a lot less likely for HK ladies to find a husband locally because of the gender imbalance, don't believe it. They are either confused or lying. The fact is: because HK men chose not to marry HK women (for various reasons), therefore there is a gender imbalance. The imbalance is not a cause to whatever phenomenon, it is merely a RESULT. Because of this choice by some men in HK, the gender ratio became imbalance. This is a significant difference. Kong girls cannot find a husband not because there are more Kong girls than Kong guys, but because Kong guys enlarged their target geographically while Kong girls did not (as much).
If one has the gender split of HK's immigration data, the myth of the gender imbalance would be easy to solve. Since I couldn't find such data, I had to do some calculation on my own. I took the population of each gender in an age group, e.g. 10-14, in 1991, "age them" by 5 year and compare with the age group 15-19 in 1996, and so on. The I calculated the % non-natural growth for each gender cohort for the years 1981-2006 (in 5 year increment). Finally I calculated the difference in these % non-natural growth. A high difference % means there is a significant difference in the non-natural growth (net immigration) between the two genders.
This is what I found.
(detailed calculation and related data (download from HK Census site) are here)
From the table, it is easy to see that the non-natural growth of female over male is much higher in the 20-40 age group. In fact, between 1991 to 2006 non-natural growth of female is higher than that of male at from 10.4% to 17.6% in the 20-30 age group.
(there are some other % that can be explained plausibly. e.g. the % in older age also shows a similar pattern, but that is because females live longer than male and therefore the base population of female is much higher, for 85+ group in 2006, female: male is 68:32. It is then not difficult to understand why the death RATE (per year, or per 5 year) for female is much lower than that of male)
p.s. (from commentator) please see pineapple farm's analysis 2 years ago (in chinese), I am basically repeating what he observed. pineapple farm also provided a link to the immigration statistics, which confirmed my hypothesis. You can see, for the 25-34 age group, women outnumbered men by around 10x, at 79499 vs 7940 from 2002 to 2006 (5 years net of 71559). From my calculation, non natural for the 5 year period is 61700 vs -3000, net=64700. The definition my be different as the age group shifts every single year plus there are immigration from other country and death/etc., so my estimate was pretty close.