Wednesday, July 11, 2012

Secularization in America: part seven


Based on 2000-2010 data from the General Social Survey (GSS), I present results of a logistic regression that measures the relationship between Internet use and religious affiliation, controlling for religious upbringing, income and socioeconomic index, year born (age), and education.

I find that moderate Internet use reduces the chance of religious affiliation by 2 percentage points (odds ratio 0.8); heavier Internet use reduces affiliation by an additional 5 percentage points (odds ratio 0.7).  Four years of college reduces affiliation by an additional 2 percentage points (odds ratio 0.8).
All reported effects are statistically significant with N=8960 respondents.

Results of logistic regression can be difficult to interpret; it might help to imagine the following progression:
  1. Start with a hypothetical baseline person raised in any religion, with moderate or high household income ($25,000 per year or more), born in 1960, with high school education but no college, and low Internet use (less than 2 hours per week): in the GSS survey, 91% of people in this category have a religious affiliation.  Now we change one variable at a time.
  2. If this person were born 10 years later (in 1970) the fraction would drop to 89%.
  3. If this person went to college, the fraction would drop to 87%
  4. If this person used the Internet 2 or more hours per week, the fraction would drop to 85%.
  5. If this person used the Internet 8 or more hours per week, the fraction would drop to 80%. 
Taken together, college education and Internet use are associated with a decrease in religious affiliation of 9 percentage points.


From 1990 to 2010 the fraction of Protestants in the U.S. population dropped from 62% to 51%; at the same time the fraction of people with no religious preference increased from 8% to 18%.  The following graph shows these trends:

In a previous article I presented evidence that something happened in the 1990s, continuing through the 2000s, that is causing disaffiliation from religion across all generations, with the largest effect on the youngest generations in the survey, people born in the 1960s and 1970s.

There are many possible explanations, but for me, the Internet pops to the top of this list.  First, the timing is at least approximately right.  Here is data from the World Bank, showing number of Internet users per hundred people in the U.S.

Internet use increased rapidly from 1995 to 2010, which is the interval of steepest change in religious affiliation.


To identify factors that contribute to disaffiliation, I ran logistic regressions with the following dependent variable:

has_relig: 1 if the respondent reported any religious affiliation when interviewed as an adult, or 0 if the respondent reported "None" (based on the GSS variable RELIG)

And these explanatory variables:

had_relig: 1 if the respondent reported being raised in a religion, 0 otherwise (based on RELIG16)

born_from_1960: year the respondent was born minus 1960 (based on AGE and survey year).  Subtracting 1960 makes it easier to interpret the results of the regression.

educ_from_12: number of years of school completed, minus 12 (based on EDUC).

somewww: 1 if the respondent reported using the Internet 2 of more hours per week, 0 otherwise (based on WWWHR, with the threshold chosen near the median)

heavywww: 1 if the respondent uses the Internet more than 8 hours per week, 0 otherwise (threshold chosen near the 75th percentile)

SEI: Socioeconomic index (a measure of occupational prestige developed by the GSS).

high_income: 1 if the respondent reports annual household income of $25,000 or more, which includes 62% of respondents who answered the question.

I used data from GSS survey years 2000, 2002, 2004, 2006, and 2010 (the relevant questions were not asked in 2008).  I excluded respondents who were not asked or did not answer one or more of the questions I used in my analysis.

It turns out that SEI does not make a contribution that is either statistically or practically significant, so I omit it from the model.

Here are the results of the model as reported by R:

                Estimate Std. Error z value Pr(>|z|)    
(Intercept)    -0.164434   0.094978  -1.731   0.0834 .  
had_relig       2.318141   0.087372  26.532  < 2e-16 ***
high_income     0.166673   0.072345   2.304   0.0212 *  
born_from_1960 -0.020161   0.002128  -9.474  < 2e-16 ***
educ_from_12   -0.051850   0.012228  -4.240 2.23e-05 ***
somewww        -0.178409   0.078490  -2.273   0.0230 *  
heavywww       -0.336658   0.080546  -4.180 2.92e-05 ***

(Dispersion parameter for binomial family taken to be 1)

    Null deviance: 7860.3  on 8959  degrees of freedom
Residual deviance: 6872.5  on 8953  degrees of freedom
AIC: 6886.5

Number of Fisher Scoring iterations: 5

All explanatory variables are statistically significant: high_income and somewww are borderline, both at p=0.02. 

The odds ratios and cumulative probabilities are:

                odds    cumulative
                ratio   probability
(Intercept) 0.85 46
  had_relig 10.16 90
high_income 1.18 91
born_from_1960 0.82 89
educ_from_12 0.81 87
    somewww 0.84 85
   heavywww 0.71 80

These results are summarized and interpreted in the Abstract, above.


As always, statistical association does not prove causation, but in this case I think there are reasons to believe that Internet use causes disaffiliation from religion:
  1. It is easy to imagine how Internet use could allow a person in a homogeneous community to find information about people of other religions (and none), and to interact with them personally.  And there is anecdotal evidence that those interactions contribute to religious disaffiliation (for example, numerous personal reports on
  2. Conversely it is harder to imagine plausible reasons why disaffiliation might cause increased Internet use (except possibly on Sunday mornings).
  3. Although it is possible that a third factor causes both disaffiliation and Internet use, that factor would also have to be new, coincidentally rising in prevalence, like the Internet, during the 1990s and 2000s.
  4. Whatever causes disaffiliation has the strongest effect on the youngest generations, which is consistent with the hypothesis that Internet use during adolescence and young adulthood has the strongest effect on religious affiliation.
So with appropriate caution, I think there is a strong case here for causation, and not just statistical association.

Furthermore, the magnitude of the effect is large enough to explain a substantial part of the observed changes in religious affiliation.  In my next article I will incorporate this regression model into the generational model I presented in Part Six, in order to estimate the effect of Internet use on these trends.

Summary of previous reports

In Part One I described trends in market share of major religions in the U.S.: since 1988, the fraction of Protestants dropped from 60% to 51%, and the fraction of people with no religious affiliation increased from 8% to 18%.

In Part Two I used data from the 1988 General Social Survey (GSS) to model transmission of religion from parent to child, and found that the model failed to predict the decrease in Protestants and the increase in Nones that occurred between 1988 and 2010.

In Part Three I looked at changes, between 1988 and 2008, in the spouse tables (which describe the tendencies of people to marry within their religions), the environment table (which describes parents' decisions about their children's religious upbringing), and the transmission table (which describes the likely outcomes for children raised within each religion).  I found that the transmission table has changed substantially since 1988, and accounts for a large part of the observed increase in Nones, but not the decrease in Protestants.

In Part Four I looked at changes in religiosity over the lifetime of respondents.  I tentatively concluded that the differences between generations were larger than changes in affiliation, within generations, over time.

But in Part Five I looked more closely and saw that all generations were becoming more religious, or staying the same, prior to 1990, and that all generations began to disaffiliate during the 1990s, continuing into the 2000s.

In Part Six I presented a generational model that retroactively "predicts" the changes we have seen since 1988, and used it to predict how those changes are likely to continue in the next 30 years.  I expect the fraction of Protestants to continue to decrease, and the fraction of Nones to increase and overtake Catholic as the second-largest affiliation by 2030.


  1. The case for internet causation looks good.
    One may also consider reverse causation (or a common prior cause):
    religiosity -> affiliation and
    religiosity -> less internet use.

    The important group are the weakly affiliated group of the 80s becoming unaffiliated in the 90s.
    This may very well be an internet (or even internet mediated adult content*) effect. The 90s hedonistic mindset creating too much of a conflict with religious narrative.
    Perhaps a less hedonistic mindset, as a result of the ongoing financial crises will promote more religious affiliation.

    * The mainstream-ification of adult content through the internet in tandem with cable TV could have created a wide chasm between religion and conservatism and non-affiliation. A group which found it easy to be affiliated in the 80s had to choose non-affiliation in the 90s to keep a consistent self-image.

    1. David, you packed a lot of interesting ideas into a short comment. Thanks!

  2. Really excellent analysis. One thing stood out though:

    "Conversely it is harder to imagine plausible reasons why disaffiliation might cause increased Internet use (except possibly on Sunday mornings)."

    It is not impossible, certainly, and to a certain degree even probable, that in communities which are homogeneous and strongly religious, that a person might feel alienated by his/her community, or may even be ostracized for his/her beliefs. This would, in turn, lead to an increase in internet usage, both as a form of stress relief and as a means of communicating with other like-minded individuals. I have seen numerous examples of people doing just this on /r/atheism because the communities they live in look down on them, or cause them undo stress from hiding their religious affiliations from their friends and families.

    While this is certainly not going to drastically alter the internet usage of non-believers in general, it is still a factor worth considering.

  3. Replies
    1. Yes! All data and code are in the Think Stats repository:

      You can check out the whole repo, or go to

      And just grab the files that start with gss. Or you can get the data straight from the GSS.

      Let me know if you find anything interesting.

  4. The thing that stands out to is the inverse relationship matching so closely between the drop in Protestantism and the rise in None (-9, +10). I'm not trying to be facetious when I ask if this internet theory of disaffiliation affects protestants harder or if this is an artifact of the larger population of Protestants. Are Jewish, Catholic, and "other" groups more immune to Internet-base disaffiliation because of stronger social ties, religious-based or possibly minority-based? Are the other populations small enough that we aren't seeing the drop as prominently?

    1. Hi Jim. Those are all good questions, so thanks! You might be interested in this report from the Pew Forum on Religion and Public Life:

      It just came out a few days ago, reports a lot of the same trends I have been writing about, and gets a little deeper into the decline in Protestantism.

      But for your particular question about what seems to be a disparate impact on Protestants, I'm afraid neither the Pew report or I have much of an answer.

  5. Very nice work. I just have one main concern: it doesn't control for time. It seems to be a given that people are using the Internet more and are becoming more disaffiliated over time. Does the significant correlation really say any more than this? Increased Internet use is obviously time-dependent, hence making the assumption that Internet use is the most significant time-dependent factor in explaining the disaffiliation seems to be a rather big assumption to me.

    It would be really interesting if Internet use in the earlier years was correlated with increased disaffiliation. Thanks for the intellectually stimulating article. I really enjoyed it. I'm not sure if I should spend the time to play around with the data (, but it is very tempting!

    1. Hi Jonathan, Thanks for a thoughtful comment. You are right that there is a danger here: disaffiliation went up in the 1990s, and so did Internet use, so naturally there is a correlation between them.

      But there are a few reasons to think that the relationship I reported is actually causative. One is that I controlled for several of the other factors that were changing during the same period, and that also contributed to disaffiliation: the big two are being raised with religion (which went down) and going to college (which went up).

      Another reason to believe that the relationship is not spurious is the "dose-response curve;" that is, the likelihood of disaffiliation goes up with Internet use. The model I reported here use two levels of Internet use; I also ran models with three levels, and found that the relationship holds up.

      It is still possible that a third factor explains both Internet use and disaffiliation, but that factor would also have to increase substantially during the 1990s and 2000s.

      If you get a chance to explore the data, let me know what you find!

    2. One factor that has increased substantially is the opposition of celebrities and other influential people to religion.

      The logistic regression model assumes that each responses is independent of the others in the sample (or that the dependence can be modeled in simple ways, as in mixed models) -- but religious affiliation and disaffiliation, like any cultural construct, is going to be highly non-linear and dependent. People react to what they perceive to be acceptable behaviour in those around them. And the example of celebrities and powerful individuals is determinative for many people.

      Typically, where religious practice dies out in a particular country, it is because the state has taken active steps to kill it off: Judaism in central Europe in the XXth century; Christianity in Russia in the XXth century; Buddhism in China under the communists (ditto Falung Gong and Christianity); Catholicism in France in the XIXth century.

      Interesting theory about the Internet. What would be the causal mechanism involved, if the Internet is not simply a confounder?

    3. Hi, and thanks for these comments. The factors I included in the model account for about half of the observed disaffiliation, leaving another half to be explained by other factors. It is certainly plausible that public opposition to religion is such a factor. If so, then it should be possible to measure that effect by comparing people with different levels of exposure to these cultural factors.

      On a technical note, the kind of exogenous factors you mentioned would affect the constant term in the logistic regression, but would not violate the assumptions of the model.