The Factors Behind the Divorce Rate in America
September 9, 2011
JESSE POWELL writes:
Divorce has risen greatly since the government began to keep reliable statistics on the subject in 1870. In 1870, the divorce rate, the number of divorces divided by the number of marriages in any given year, was a mere 3.3 percent. This rate rose to 8.1 percent in 1900 and to 13.4 percent in 1920. The divorce rate rose continually in America from 1870 up until 1975, when it hit near 50 percent, and then, mysteriously, stopped rising any further. All the way from 1975 up until 2009, the most recent year available, the divorce rate has remained remarkably constant hovering around 50 percent during the entire time.
Does this mean that family life in America as regards the issue of marriage and divorce is now stable? Did America enter a permanent plateau in its divorce rate after this rate had risen continuously for 100 years?
The first thing I wish to point out is that prolonged stability in any social indicator, especially one as important as divorce, is highly abnormal. The cultural environment in America at the present time is anything but stable so an indicator such as the divorce rate being stable over an extended period of time is almost certainly due to conflicting forces working against each other that balance each other out. What is happening on the surface appears to be stable but what is happening underneath the surface certainly is in a process of great change.
The divorce rate is a composite of three different independent variables: 1) What proportion of the marriageable age population is married? 2) What is the likelihood of someone who is now single getting married? and 3) What is the likelihood of someone who is now married getting divorced? If you know these three ratios you can calculate the divorce rate.
From a purely mathematical point of view the divorce rate increases when the population that is married increases as only people who are already married can get divorced. Likewise the divorce rate decreases when the population of single people goes up as only single people can get married. When the propensity to divorce goes up (the likelihood of an already married couple getting divorced in any particular year) then the divorce rate goes up; likewise the divorce rate goes down when the propensity to marry goes up.
Over the past 35 years, the divorce rate has hardly changed at all; the question is, what has happened to the three underlying factors of the divorce rate since 1975?
Below is a table giving the underlying factors behind the history of the divorce rate in the United States since 1920.
The labels in the table are: %Mar (Percent Married, the proportion of the marriage age population; that is 14 and over from 1920 to 1970 and 18 and over from 1970 to 2009; that is married); Div/Prob (Divorce Probability, the probability per year that a person who is currently married will get divorced); Mar/Prob (Marriage Probability, the probability per year that a person who is currently single will get married); Div. Rate (Divorce Rate, the number of divorces divided by the number of marriages in the given year)
The letter “a” attached to the years from 1920 to 1970 indicate the population under consideration is 14 and over. The letter “b” attached to the years from 1970 to 2009 indicates the population under consideration is 18 and over. There is a sharp increase in the Percent Married and the Marriage Probability going from 1970a to 1970b; this is because the population under consideration is reduced from those 14 and over to those 18 and over.
%Mar 
Div/Prob 
Mar/Prob 
Div. Rate 

1920a  58.3%  0.79%  8.25%  13.4% 
1950a  67.1%  1.03%  9.06%  23.1% 
1955a  68.4%  0.95%  8.34%  24.6% 
1960a  67.3%  0.93%  7.41%  25.8% 
1965a  65.8%  1.07%  7.76%  26.6% 
1970a  63.4%  1.50%  7.89%  32.8% 
1970b  71.7%  1.49%  11.51%  32.8% 
1975b  69.6%  2.08%  9.90%  48.1% 
1980b  65.6%  2.27%  8.71%  49.7% 
1985b  63.0%  2.21%  7.60%  49.3% 
1990b  61.9%  2.10%  7.06%  48.4% 
1995b  60.9%  2.00%  6.24%  50.0% 
2000b  59.5%  1.89%  5.67%  49.1% 
2005b  58.7%  1.68%  5.01%  47.7% 
2009b  57.4%  1.63%  4.31%  51.1% 
The next table shows more clearly how each factor contributes to the change in the divorce rate from one period to the next. The numbers in the row indicating the year 1920 are all zero because there is no year prior to 1920 in the table; the change from 1920 to itself is zero. The next row, 1950, has the number positive 54 under the “%Mar” column. This indicates that from 1920 (the prior year in the table) to 1950 the change in the Percent Married (the number of married people compared to the number of single people) greatly increased the divorce rate over what it would have otherwise been if there had been no change in the Percent Married category compared to the prior year. The number 54 represents the quantity of increase the change in the Percent Married ratio added to the divorce rate. The 54 number represents 54 units of increase to the divorce rate; a unit of increase being oneone hundredth (0.01) of a doubling where each unit of increase adds the same proportion to the divorce rate (a single unit of increase increasing the divorce rate by 0.70%). In this table the “1970b” row is eliminated since the associated changes are caused entirely by the change in definition of the marriageable age from 14 and over to 18 and over (in the 1970b row the %Mar increases by 55 units, the Mar/Prob decreases by 54 units, the Div/Prob decreases very slightly rounding to 0, and the Div. Rate is not changed at all).

%Mar 
Div/Prob 
Mar/Prob 
Div. Rate 
1920a  0  0  0  0 
1950a  54  38  14  78 
1955a  9  12  12  9 
1960a  8  3  17  7 
1965a  9  20  7  4 
1970a  15  48  2  30 
1975b  14  48  22  55 
1980b  27  13  19  5 
1985b  17  4  20  1 
1990b  6  7  11  3 
1995b  6  7  18  5 
2000b  8  8  14  3 
2005b  5  17  18  4 
2009b  7  5  22  10 
One can see from the above table that marital composition (the %Mar column) has decreased the divorce rate relentlessly since 1955 (meaning the proportion of single people has increased continuously since that time). Indeed, if the proportion of adults being married stayed constant from 1955 to 2009 while the propensity to marry and divorce remained at their 2009 levels the divorce rate would have been 120.1 percent instead of the actual 51.1 percent. The proportion of single adults surged particularly strongly from 1965 to 1985 due to the sharp increases in the propensity to divorce that occurred from 1960 to 1980. There was a decrease in the propensity to marry in the 1950s followed by a relatively small increase in the 1960s. Starting in 1970 however the decline in the propensity to marry has been relentless and rather fast; from 1970 to 2009 the probability of a single adult getting married in any particular year has fallen from 11.5 percent to 4.3 percent; an increase in the average duration of being single from 8.7 years to 23.2 years. The overall pattern in the three factors contributing to the divorce rate has been rather stable since 1985. Basically, the strong decrease in the propensity to marry has been offset partially by the continuing decrease in the propensity to divorce and the continuing increase in the proportion of the population that is single. These three factors added together balance each other out resulting in the divorce rate being largely unchanged over the period.
Sources: “The Culture War and Working Women,” The Thinking Housewife, February 3, 2011; National Marriage and Divorce Rate Trends ; Statistical Abstract of the United States,2011 Statistical Abstract: Earlier Editions.
— Comments —
Laura to Jesse Powell:
Are widows and widowers included in your figures for those who are single?
Mr. Powell writes:
In the above tables everybody above marriageable age is counted as either married or single, you can think of the categories as being married and notmarried. This means that widows are counted as being single just like all other singles.
The data I used in the tables above for the years 1970 (1970b) and 2009 is below:
Married 
Single 
Marriages 
Divorces 

1970  95,000  37,500  2,159  708 
2009  130,300  96,600  2,080  1,063 
Below is information on the number of widows (both male and female) and the number of excess females (the number of women in excess of the number of men) for 1970 and 2009:
Widows 
Excess Females 

1970  11,800  7,500 
2009  14,200  6,900 
Below is the adjusted data if widows were excluded from the Single category and all marriages were assumed to not involve widows (this adjustment will not affect the divorce rate at all):
All adults not married are considered to be single:

%Mar 
Div/Prob 
Mar/Prob 
1970  71.7%  1.49%  11.51% 
2009  57.4%  1.63%  4.31% 
Widows both male and female are excluded from the singles population and are not counted in the below:
%Mar 
Div/Prob 
Mar/Prob 

1970  78.7%  1.49%  16.80% 
2009  61.3%  1.63%  5.05% 
Widows as a proportion of the singles population declined from 1970 to 2009 going from 31% of all singles to 15% of all singles. If one excludes widows from the population of single people the decline in the proportion of married people and the fall in the propensity to marry becomes more severe.