Selection Effects: What's at Stake? (following up on The National Marriage Project Report "Before I Do")

See the prior post (below) for more information on the National Marriage Project Report that Galena Rhoades and I authored that was released yesterday.

I want to make you aware of a couple of pieces we've written on the important issue of "selection effects." You'll often hear social scientists talk about this subject when they discuss or critique the type of findings we present in the Before I Do report. The subject is important because it revolves around the degree to which scientists believe that some experiences in life are causally related to outcomes in life.

So, you have a couple of options, if you want to read more on this subject.

For a briefer (about 2.5 pages) take, linked directly to the NMP release, check out what we just posted at the Institute for Family Studies website:  Selection Effects and Personal Choice

For a longer (about 4 pages), more general take, with similar observations but also a deeper set of questions about the problems of free will in science, see this one:  Selection Effects: Social Science and Personal Choices

If you like going deeper on such issues, there you go.

Marriage and Cohabitation: Another Take, Building on the Discussion of Selection

[This was written years ago. Since this one is pretty popular, I have updated links now with various studies as of 2-2015. Also, if you are interested in the subject of cohabitation and want a narrative summary of our line of research, complete with abstracts and citations and how we were thinking in the progression of studies, you can get a document on that, here.]

This post is about cohabitation and marriage and commitment. It is also the last of five posts on key scientific issues that affect all of science, social science, and have been huge issues in discussions and debates about cohabitation. I plan for this one to be the last major, heavy science piece on those themes for awhile. For full context, see preceding posts.

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Backdrop for the Blog Entry Below

The Institute for American Values and the National Marriage Project just released the third edition of a report entitled Why Marriage Matters. It is a document authored by sociologist Brad Wilcox, who heads up the National Marriage Project, and co-signed by a group of family scholars, including myself. You can find out more about the report, order a copy, or download the press release, executive summary, endnotes (all the references cited) by clicking on the title above.

The report created quite a stir, and reignited the continual debate among scholars about the importance of marriage and the implications of cohabitation. One particularly strong example of the debate on such matters comes from the blog of sociologist Philip Cohen. You can see Cohen’s comments on the issues as well as comments from various people in reply, including Brad Wilcox and other family scholars, on his site by clicking here. There are follow-ups in the next blog entry of Cohen, as well.

In thinking about the various issues raised in the Why Marriage Matters report as well as on Cohen’s blog and elsewhere, I wrote the following thoughts. So, here you go. Plenty to chew on and think about.

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My Thoughts

Every responsible scientist in the family field understands that there are potent selection factors involved in romantic trajectories and family outcomes. Further, the income/education/poverty aspects of selection are particularly compelling and raise concerns about how individuals’ aspirations can get hammered by environments. In comparison to sociology, though, psychologists like me have an orientation toward intervention at the individual level while accepting selection. To many of us, evidence for selection is knowledge that can be used to identify people at greatest risk who may need help more than others. For example, there must be a large amount of selection involved in having low birth weight babies. Such knowledge can be used to guide policy at the macro level while also informing what to try to change at the micro, individual level. One of the concerns that I (and colleagues like Galena Rhoades) have is that selection is too often taken to imply that only the macro, societal level of risk matters. I think there is a bias in sociology in this direction because the scientists are primed to think about macro effects.

In terms of cohabitation and selection, my colleagues (Galena Rhoades & Howard Markman) and I find that you can robustly control for selection and still demonstrate risks associated with cohabiting prior to engagement (the risk of cohabiting prior to marriage appears to be clearly moderated by this). That’s not to say that we’re done studying this. We would particularly like to get longer-term marital and cohabiting outcomes in a large, national longitudinal sample we have wherein we measure a massive number of potential selection variables along with relationship status changes, relationship quality, and information about how transitions occur. Regarding the latter, we originally began to test for the presence or absence of mutual plans for marriage at the time cohabiting begins based on a theory we have that cohabitation has more inertia for continuance than dating without cohabiting. In other words, what people often miss in thinking about cohabitation is that it makes it harder to break up (once you share a single address). Yes, people are quite likely to break-up in cohabitation, but that’s in comparison to marriage. The comparison to dating is more apt for understanding some of the issues involved. [Update 2-2015: Website for official journal article is here. PDF of manuscript in form I can post it is here.]

For many, moving in together allows constraints to build prior to the development of mutual, or at least clear, dedication between the partners. We have shown in a number of studies that constraints build up steadily in cohabitation and that constraints predict relationship stability net of dedication. In the latest analyses, we examine changes resulting from the transition to cohabitation using within-subjects analyses (providing a strong control for selection). Among a myriad of findings, the analyses show that constraints take a marked jump up in level at cohabitation and then start to grow at a faster pace during cohabitation. (Update 2-2015: This paper is published.)

This brings me to one key point I’d raise related to the flurry of postings on Philip Cohen's site. Cohabitation often occurs well before marital intentions are mutually clear and public. This means that, for many couples, various forces to remain together (constraints) increase earlier in the mate selection or pair-bonding process than before, at least in modern history. Further, the type of cohabitation we believe is most associated with risk from inertia is now the most common [Link added, 2-2015] (cohabitation prior to mutual plans to marry). (For those who would want to take marriage and/or engagement out of the picture in thinking about risk, simply insert the idea that the commitment to the future—its mutuality and symmetry—is important prior to going through a transition that is potentially constraining. Like transitions into cohabitation or having a child.)

There is a lot of selection involved in who cohabits prior to having clear, mutual plans for marriage. However, on top of those selection characteristics, cohabitation adds to the picture by making some of these already riskier relationships harder to leave. This does not prevent a child from being born to two cohabiting parents. With more children being born and raised in cohabitation, children increasingly are in homes with parents who are in higher risk relationships that have, on average, lower levels of dedication and other characteristics of higher risk. There are, of course, marriages with the same characteristics and there are many cohabiting unions without these characteristics. However, on balance, we believe cohabitation plays a causal role in risk on top of selection because of the increased constraints inherent in it. (And for some people, cohabitation likely lowers their risks, though this is more challenging to demonstrate.)

This model of cohabitation risk based on inertia fully embraces selection. In this way of thinking, cohabitation may not causes poorer parenting but it may well increase the number of couples who have or bear children who are not well matched and who will have difficulty parenting together. Hence, one can predict that a net societal increase in cohabitation that begins before partners have a clear and mutual commitment will lead to a greater number of children living in difficult contexts.

Serial cohabitation is illustrative of some points about selection at one level and individual choice at another level. Serial cohabitation is associated with later difficulties in marriage and/or family stability. Selection is involved (on average, it’s more likely for those growing up in a single parent home, those with economic disadvantage, etc.). A person who has those and other background factors is definitely at higher risk no matter if they cohabit with a number of people or not. Yet, does it seem far-fetched to suggest also that a person with such background risks can improve their odds if they raise the bar on conditions under which they would begin to cohabit with someone (e.g., strong mutual commitment, engagement, or marriage)? In line with inertia, a person doing so would make it less likely she or he will get stuck, at least for a while, in a difficult spot. More importantly, if a single parent avoids extra cohabiting relationships, they also reduce the degree to which their children are exposed to significant attachments that end. Further, there is reason to believe that such a person could reduce the possibility of child maltreatment since the odds of that occurring are greater with live-in partners. Even with selection, a person making such adjustments in their personal life is changing here-and-now behavior that matters. Fortunately, this is one area where experiments may show if the chain of logic holds up. Such an experiment was designed by my colleague Galena Rhoades, but it is, as yet, unfunded.

That brings me to the matter of cultural and dyadic aspects of commitment. There are reasons why marriage, including the ceremony, actually should matter regarding outcomes. This can be debated endlessly, of course. A conceptual rationale may be the best we can do here, since this is not an area where any of us are going to get to do an experiment and randomly assign people to marriage and not marriage.

First, marriage signals a lot about commitment. While marriages are much weaker than they used to be, at least in terms of stability, part of what I believe is protective about marriage is that it conveys a less ambiguous signal about commitment than that conveyed by cohabitation. This matter of signals was becoming a big focus in Steve Nock’s work before he passed on, and, what I am pretty sure was his last published writing was focused on exactly this (see references link below). At the same time that Steve Nock was focusing more on signals, spurred on by the ideas of economist Robert Rowthorn, I had been focusing on what I saw as a decline, in general, of emblems of commitment in changing patterns of how people mate. Nock and I, along with numerous others, all thought these changes were consequential. Andrew Cherlin has suggested that marriage has become a status symbol, economically, denoting wealth. That seems true. But, more importantly, I think, marriage remains the strongest culturally imbued signal of commitment status even in weakened forms. [2-2015 update: For a piece dealing with the issue of the timing and sequencing of signals, I lay this out clearly, here.]

In our work, we have found that when cohabiting is not preceded by mutual clarity about a commitment to the future (e.g., by engagement or marriage), there is not only evidence of lower relationship quality, there is a greater likelihood of asymmetry in dedication levels between partners. I see this as part of a scientific explanation for why books like “He’s Just Not That Into You” are bestsellers. One of protective things about publicly understood (and institutionalized) signals like engagement and marriage is that they require both partners to declare their commitment levels—and I particularly mean commitment as dedication, here. [Update 2-2015: For more on this theme, see our article here.] Without cultural forms that push this information out in the open, it is easier to have relationships where one partner does not fully realize that the other is substantially less committed. The emergence of new cultural forms like FaceBook’s relationship status indicator may start to fill a gap by providing a commitment clarifying tool for some couples.

I do, by the way, believe that cohabitation can signal higher levels of commitment (compared to not cohabiting) among some who are very poor. I think it likely that the potency of a signal is partially related to what other signals are available. For many complex reasons, marriage is so far off the radar screen in terms of experience for many in poverty that another signal like cohabitation can take on signal value. But, more generally, it seems that cohabitation conveys very little information about the level of commitment in romantic relationships. That’s why, for example, we find that infidelity is no less likely in cohabiting relationships than in dating relationships. This is not to say that cohabiting partners cannot have high levels of dedication to one another. Many do. Further, while marriage requires public clarity about commitment and cohabitation does not, a cohabiting couple can talk about their relationship and clarify commitment between them and to others. But most do not do these things, and, in fact, most cohabiting couples slide into cohabiting without discussing what it means (for more on this, see the note in the references link below). This is part and parcel with Steve Nock’s observation that cohabitation is not an institution with specific, common meanings.

Second, let’s think about the matter of ceremony as raised by Brad Wilcox. I am not a social psychologist, but it is easy to call upon that field’s robust literature of experimental studies that test the likelihood of people following through on commitments made under varying conditions. The cognitive dissonance literature is replete with evidence that the strongest action tendencies are set up by the awareness that one is making a clear choice among two or more alternatives. Further, based on the power of a desire for cognitive consistency, the more publicly one has declared their decision, the stronger the set up for following through. These are powerful human tendencies demonstrated in scores of studies. What aspects of cohabitation (when not accompanied by commitment to marriage) perform these functions? Marriage is a cultural phenomenon that, whatever else may be true, has historically required the very kinds of behaviors that a lot of science suggests will affect persistence to follow through.

To sum up, I believe that scholars can accept and respect the evidence for selection while also maintaining that there are strong, protective aspects to marriage.


References Centrally Related to this Post (click here)

For something more lighthearted, but meaningful, about personal decisions in one's romantic life, see my older post on black jack and roulette (click here).

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Do Actors Act? Further Thoughts on Science, Selection, and Free Will

[NOTE: This is the fourth in a series on science, free-will, and selection. So if you’ve not read the last three entries, I recommend you do because they build up to this one. It’s a lot to read, I know, and this is the longest entry I am writing on this subject, but it’s all got to be said in one chunk.]

I last suggested that one might be able to show that teens can get sexually transmitted diseases without ever touching other humans. I do not mean that one can get a STD without some type of sexual contact. I mean that a social scientist might be able to get close to presenting a convincing case for something that is not possible. And, to be sure, I am exaggerating. But I exaggerate with a purpose, and it is not to be flip.

Recall what a social scientist means by a selection effect. There is a great deal of evidence of selection in numerous kinds of risk that people have in life, including in their love lives. Some of the most important selection effects are related to family history, poverty, and education. For example, people who cohabit with a number of different people before marriage are likely to have more trouble in marriage than those who do not, and they are also more likely to have selection factors like those I just listed. The interesting question is whether or not cohabiting with a number of people actually makes it more likely people will struggle in their marriages or if the other background risks simply lead to both the serial cohabitation and problems succeeding in marriage. Or both. You would not do too poorly in life to usually bet on “both” when dealing with questions like this.

My colleague Galena Rhoades and I talk about this a great deal because it affects what social scientists covey to others about what can and cannot change in their lives. I’ll get to that later after we have some fun with imaginary data.

AN EXAMPLE

Okay, now to sex. I know you have been waiting patiently. Assume you are a researcher studying sexually transmitted diseases in older teenagers. In fact, you have the most amazing data set in the history of your field. You have a sample where you know a stunning number of things. On the 25,000 people in your sample, you have measured these variables and more: family history, parental relationship quality, parental divorce (or, if parents ever married), the number of romantic relationship transitions each parent has had (and at what ages for the individuals in the sample), levels of parental supervision, personal insecurities, personality tendencies to seek stimulation and impulsivity, drug use history, alcohol use, school performance, the number of sexually active kids in each individuals’ school and neighborhood, physical health, everything else about the neighborhood including crime, stress, social integration/disintegration, resources, sex-and-stress-hormones like daily (I mean to be extreme here) blood levels of androgens and estrogen, oxytocin levels and reactivity to it, vasopressin levels, parents income, current household income, parents’ education levels, religious beliefs, religiousness, beliefs about sex, type and number of friends, specific genetic markers associated with sexual behavior and pair bonding (are you getting tired of this list yet?) . . . Okay, I’ll stop. But, please assume I could have gone on for a while because I could have.

By the way, you have a huge budget.  Huge.  And a massive sample size.  Massive. You have followed this sample from age 12 to 20. You and your assistants check in with each of the individuals, relentlessly, and you also have access to all kinds of records. And, you’ve not lost contact with too many people. It’s a dream data set (and it would be very expensive). You also know who has had sex, when, with whom, what type of sex, and under what circumstances. (Those GPS circuits in cell phones are really rather amazing.) You also know who has had, or continues to have, an STD. Let’s also assume that the data are really good with low measurement error; however, you also must assume that sexual behavior is pretty sensitive stuff to most people, and it’s a little fuzzier than most of the other measurements you have as to error. But still, you have very good information on sexual behavior.

It’s statistical time. Your first question is about selection. How much of the STD risk do all these variables, except for sexual behavior, explain? You crunch the data and find that you can explain 75% of the differences between individuals who get and do not get STDs. Pretty amazing (though, realize it’s harder to explain as much as a prediction, using the same variables, in a new data set—technical point you can ignore if you like). Now, you do another, similar analysis but you add the sexual behavior variables into the stew. Suppose the amount of variance explained goes up 80%. Wow. That’s a lot of explanation. You are happy because you will get this published and it’s actually kind of useful information.

Please keep in mind I’m making up an example, here. These are not real findings.

Why doesn’t the amount of variance explained shoot up a lot higher when you throw in the sexual behavior variables? In this case, it only goes up a bit higher because the selection variables explain so much, there is not a lot else to explain. Your big bunch of selection variables was so good at “predicting” who would get an STD that you hardly need to know whether or not, and when and how, people had sex. In fact, that whole having sex thing looks pretty inconsequential based on the analyses.This is an extreme example but the point I am making is that when it comes to come common behaviors and risks, there truly are a lot of background variables and factors that seem to determine the outcome. 

Quiz. Does the fact that you have just shown that selection explains a ton about who gets STDs mean that teens can get STDs without ever having sexual contact? Of course not. While we are here, I want to make a couple of complicated points. If you want to skip ahead, just move on to “three points to ponder” below.

COMPLEX BITS

First, as a risk behavior becomes something more and more people do, it, ironically, becomes harder to detect it as mattering in risk outcomes. Extreme examples are extremely useful. If 93% of people do some behavior that is risky, the fact that you have almost no one to compare the 93% to makes it pretty hard to show that the behavior matters. Plus, the 7% will be quite unusual, making what you can conclude from the comparison of limited value. Let that sink in a bit.

Second, I’m using terms here like “risk behavior” a lot here, but doing so is complicated because one of the core issues in this discussion is whether or not a behavior associated with risk is truly risky behavior. In the case of a hookup with a stranger at a party, it’s pretty obvious that the behavior is risky, no matter what else is true. That’s the point of my STD example above. But here is a different example. Serial cohabitation is associated with later difficulties in marriage and/or family stability, and, of course, there is some selection involved (on average, it’s more likely for those growing up in a single parent home, those with economic disadvantage, etc.). A person who has those and other background factors is definitely at higher risk no matter if they cohabit with a number of people or not. Yet, isn’t it pretty obvious that a person with such background factors improves their odds if they do not cohabit before marriage or they cohabit only with one person, and only after having mutual plans to marry or some other really clear clarification about commitment?

I say this because by not having those extra cohabiting relationships, the person makes it less likely they will get stuck, at least for a while, in a difficult spot. That’s because constraints to remain together are greater when cohabiting, and that makes it harder to leave. If a single parent avoids extra cohabiting relationships, they also reduce the degree to which their children are exposed to significant attachments that end. Further, there is reason to believe that such a person could reduce the possibility of child maltreatment since the odds of that occurring are greater with live-in partners. Even with selection, a person making such adjustments in their life is changing here-and-now behavior that matters.

THREE POINTS TO PONDER: CAN ACTORS ACT?

Back to you and your amazing, fantasy data set and astounding evidence for selection. (Yes, researchers have fantasies about data sets. There, I’ve let the secret out. You might think you’ve heard about all the temptations on the web, but do you know there are some data sets out there on the web that anyone can access? I know, I should not tempt you.) So, now you have your findings and you present them to the world. You can very easily sound like you are saying that the actual sexual behavior of the teens didn’t matter much in producing risk. You’d be right in a way and way, way off in another way.

First, selection matters and it is everywhere. In fact, it’s closely related to what social psychologists call the fundamental attribution error. It has been repeatedly proven that we (all of us, really) tend to over attribute the causes of other peoples’ behavior to themselves and give far too little weight to their circumstances. (We happen to generously give ourselves credit for how circumstances affected what we did when we have done something wrong or poorly. Neat trick, that.) That’s why popular sayings like “walk a mile in their shoes” have real scientific oomph behind them. Environments matter, as does selection.

Second, social scientists have a difficult time figuring out how much of a risk effect to ascribe to selection and how much to experience. We can get close, but it’s hard to ever totally answer this question. One of the common ways to figure out if experience (versus selection) actually matters is to assess a massive amount of potential selection variables and see if experience still explains anything. This is an imperfect but credible and important approach to teasing selection and experience apart. This is one of the things we do in our research on cohabitation, particularly in one large sample we are following over time. We measure an amazing number of possible selection variables to “see” how much experience matters. There are other strategies one can pursue, as well.

Third, and a SUPER BIG SOCIAL SCIENCE DILEMMA: It’s not all that clear how researchers can actually measure whether or not people have the option to engage in, or not to engage in, a behavior associated with higher risk. You can measure if risky behavior happened. You can measure what background characteristics make it more likely that behavior will happen. But, you cannot easily measure if someone had a choice.There are some ways to get close to measuring choice, but they involve very creative experiments, and these are not the kind of data most debates about selection and experience revolve around. So, while it’s hard to demonstrate that people actually make choices, and, thereby, show they have choices to make, it’s pretty easy to get evidence for selection. But how do you even keep evidence of free-will and choice in your statistical model? This means social scientists can often sound like the individual's ability to decide or choose is not part of what matters. This is a profoundly important question (unless I’m missing something really obvious to another who will eventually point it out to me.  That happens plenty often and I’m fine with it!).

An emphasis on selection can be motivated by good science and it can also be motivated by compassion and social justice concerns. This is because, in most things where it comes up, selection implies that individuals have disadvantages that contribute to how things turned out. But here’s the downside of so strongly emphasizing selection, as is truly, commonly done is social science. The misleading message carried in the DNA of selection is that you—the individual—can’t really do anything to control your odds of success in life. It’s out of your hands. And this is the greatest concern Galena Rhoades and I have identified in thinking deeply about this issue: while it’s important to take into account the hand someone has been dealt in life, it’s also important to look for ways to help that person play the hand they have as well as they can.It is important not to convey that they are helpless victims and cannot do anything that affects their own outcomes.

Very strong selection-based story lines tilt the whole board toward implying our behavior is determined somewhere other than in our decider circuits. Is that what most social scientists really have in mind when they emphasizing selection? I doubt it, but that is the implication of the message.

Sure, some people have selection factors that make it harder to choose, or even have access to, a lower risk pathway in life. But do we want to accept the idea that our here-and-now behaviors, in some of the most important areas of life, are out of our control? I choose not to believe this.


For the practical implications of how what someone believes in such matters can affect his or her love-life, see my post on gambling from last year. When you are up for reading more, that is.

Click here:
Black Jack Or Roulette? You Choose

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Selection and Science: Cohabitation Research as the Example

I’m going to build on the last two posts about science by focusing in on a related topic that is of great importance in my own field of study—that is, the study of romantic relationships. I want to start by giving you the definition of a selection effect in social science. I’ll start with an example. While it’s less clear than it used to be, decades of studies show that those who live together prior to marriage are less likely, not more, to do well in marriage. This finding keeps making headlines because the historical pattern has been very counterintuitive. After all, most people believe that one of the best ways to improve your odds in marriage is to live together before marriage. I used to say most “young” people believe this, but now it’s really most people of all ages, including the parents of people who are currently young. (More recently, by the way, it is the presumed absence of this finding that has been making headlines.)

There is a complicated debate going on among social scientists how as to whether or not this cohabitation effect is going away as cohabitation before marriage becomes the norm. I think the reports of its demise are premature. Nevertheless, if you are interested in the current findings, our work consistently shows that people who only cohabit after they are engaged or wait until marriage are at lower risk than those who cohabit before there are clear, mutual plans for marriage. That word “mutual” is pretty crucial, here. Sometime, I’ll come back to why that latter finding is very important and what theory it was predicted by before we started to test for it. Suffice for the moment that we have published many studies now with different data sets showing that cohabiting prior to engagement is associated with greater risks in marriage. Personally, I think it’s best to wait until marriage, but if one does not plan to do that, I think it’s wisest to at least be engaged, first.

Okay, that’s not really what I wanted to write about. It just sets the stage. I want to write about selection effects and here I go. The classic explanation for why cohabiting before marriage has been associated with poorer outcomes in marriage, not better, is selection effects. Selection means that there are characteristics associated with certain people that are both related to the risk you are interested in (in this case, doing less well in marriage) but also more associated with the likelihood of doing something like cohabiting prior to marriage that appears to cause risk. Are you still with me? Historically, one could have looked at all the research showing cohabiting before marriage may not be the panacea it’s cracked up to be and suggest that cohabiting prior to marriage actually harm relationships. The counter view is that the cohabiting itself has nothing to do with the eventual outcomes but that it’s the people who were more likely to cohabit—they were more risky to begin with, and they ‘d have been more risky whether or not they had cohabited prior to marriage.

There is a lot of evidence of selection effects in various types of analyses of risk in social sciences. In the case of cohabitation, those who are most likely to cohabit truly are less religious, less traditional, more likely to come from homes where their parents divorced (or never married), more likely to have a lack of confidence in marriage, more likely to have children from prior partners, have had more sexual partners in the past, and are less educated (just name a few things associated with selection). These factors are associated with more problems in marriage and they are associated with greater likelihood of cohabiting prior to marriage (and a much greater likelihood of cohabiting prior to engagement). The idea is that these folks are already “select” for risk in marriage, and they are also more likely to “select” cohabitation prior to marriage or prior to engagement. That’s a selection effect. When a social scientist uses the term, they mean to suggest that what you might have thought was the element causing risk is not causing the risk at all. Selection variables are actually causally linked to risks and outcomes. What I mean here is that selection effects are not the part of the risk that is causal as in related to the behavior in focus—cohabiting before marriage or before engagement.[1] It was already baked in and it just looks like that variable is causal.

Here’s the problem with selection and here’s where this post links to the past two posts about science and materialism (the view that everything that is, is material; and if enough of what’s around is was measured accurately and analyzed correctly, you could explain anything). I believe that selection has the same tie as much thought in other areas of science to the logical extension that people have no free will. You may think I exaggerate, but keep thinking it through. It is where the assumptions lead. In this case of cohabitation, you might think that you decide whether or not to cohabit before marriage or engagement, but in reality, selection says that such things were pretty determined long ago by the behavior of your parents and the setting of your birth and upbringing, and the opportunities these things provided or failed to provide.

My colleague Galena Rhoades and I (along with our colleague Howard Markman) have shown in numerous studies that, even if you “control” for scads of selection variables (scads is scientific speak for a large number), you still can show a clear risk for cohabiting prior to engagement. With selection massively controlled for, such findings provide some evidence suggesting that there is something about the experience of cohabiting that is causing risk on top of the selection into the risky pathway. Ah, but hold the fort (I suppose that means, don’t abandon your position too quickly). If you are a modern day scientist, and you deeply believe that better measurement ultimately causes more thing to be explainable, you would not take studies controlling for known selection variables as evidence of the behavior being risky but, instead, as evidence that you have not yet figured out all the other selection variables to measure in order to wipe any sense that there could be something causal to cohabiting prior to engagement or marriage. This idea is analogous to a scene in one of the Star Wars movies. Remember when the good guys are “flying” through the sea in a submersible, and a giant fish of a sort starts snapping after their little boat, and then a larger, even more giantish fishlike sea creature comes out of a hole to bite down on the large fish pursuing the good guys? Crunch. Qui-Gon Jinn says: “There's always a bigger fish.” A scientist often believes the same (often, rightly so, by the way): There is always another variable or set of variables that, if properly measured, explain what is not yet explained or incorrectly explained.

I will stop here for now but stay tuned. Next, I’m going to argue for how science might be able to show that a person could get a sexually transmitted disease without every touching another human being. And I don’t mean from a toilet seat. I mean to use that point to highlight a problem science has with measuring and analyzing free will. For now, I'll keep a lid on it.

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[1] I added the clarity here about selection playing a causal role but not in the way people wonder about the effects of cohabitation, in February 2016.

If you are interested in some of our publications related to cohabitation, here are a few citations.

Kline (Rhoades), G. H., Stanley, S. M., Markman, H. J., Olmos-Gallo, P. A., St. Peters, M., Whitton, S. W., & Prado, L. (2004). Timing is everything: Pre-engagement cohabitation and increased risk for poor marital outcomes. Journal of Family Psychology, 18, 311-318.

Rhoades, G. K., Stanley, S. M., & Markman, H. J. (2009). The pre-engagement cohabitation effect: A replication and extension of previous findings. Journal of Family Psychology, 23, 107-111.

Stanley, S. M., Rhoades, G. K., & Markman, H. J. (2006). Sliding vs. Deciding: Inertia and the premarital cohabitation effect. Family Relations, 55, 499 - 509.

Stanley, S. M., Rhoades, G. K., Amato, P. R., Markman, H. J., & Johnson, C. A. (2010). The timing of cohabitation and engagement: Impact on first and second marriages. Journal of Marriage and Family, 72, 906-918.