The Problem With Infant Sleep Training Research

Sleep training.

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A polarizing topic that has the ability to invoke anger, shame, guilt, confusion, and judgment all in one. A topic riddled with misinformation and one sided truths. My goal with this post is to discuss some of the problems with the available infant sleep/sleep training research.

Before we dive in, I want to start by saying a couple of things. First, I whole heartedly believe that all parents must make the best choices for themselves and for their families. This post is not meant to shame or judge anyone. You do not have to defend your parenting choices to me or anyone else.

Second, I define sleep training as teaching or training a baby to sleep, and often, to eat, wake, and be comforted based on some timeline that goes against their, and your, natural patterns, rhythms, and instincts. This includes any and all methods that you do not feel right to you and cause distress in your baby.

Now that I’ve said that, let’s first look at research in general.

What is Research?

Research is a dynamic process designed to discover new knowledge, find meaning, foster ideas, and gain insight. In order to accomplish this, research must be critically evaluated, replicated, refuted, and/or expanded. In other words, research is always subject to change. It’s never perfect and it’s never black and white. This is particularly true when researching human behaviour given the nuance and complexity attached to human beings. However, quality and quantity allow us to get as close to the truth as possible. That is, the stronger the study and the more the study is replicated with similar findings, the more confident we can be in the initial results. Even then, there’s always room improvement.

Research is always critically evaluated and always has limitations. There is always a better method, more participants to include, more defined measures, a better way to ask questions, a different method of analysis…Not to mention, the possibility of bias and confounding variables. Research is never perfect, and it’s not meant to be. This doesn’t mean that research shouldn’t be trusted or utilized. No, even poorly designed studies or studies that have been refuted contribute to the larger body of research. My point is that research must be viewed with a critical eye. It’s not necessarily about the results, but how the results were derived.

With that said, let’s apply this critical eye to sleep training research.

Sleep Training Research

I’m not going to review every study conducted on infant sleep, although, it may be fun to do so at some point. What I am going to do is give a general overview of some common issues with the available research on infant sleep and sleep training.

First, the majority of studies are parent report. In other words, the parent is giving their observation and perception of their baby’s sleep. Parent report is a subjective measure prone to inaccuracies. A more objective measure would have babies sleeping in labs directly observed by the researchers or using video observation. An even better measure would be actigraphy, which is a monitor that measures human rest and activity cycles. What some preliminary studies have found is that while the parent reports more sleep and less wakes, the baby’s sleep behaviour remains unchanged. That is, babies are still waking, but they’re not signalling (i.e., crying). Really, the effect is found in the parent, rather than in the baby.

Second, a lot of infant sleep studies have small sample sizes (e.g., 40-60 participants). It is difficult to draw accurate conclusions representative of the larger population when the number of participants is so small.

Third, most studies aren’t longitudinal, which means that they aren’t conducted over a long period of time. Given that one of the issues is whether sleep training negatively impacts children in some way, it is important to conduct studies over a long period of time (e.g., into adulthood) in order gain a more comprehensive view.

Fourth, the majority of these studies stem from a behaviourist view point. In other words, doing something to elicit or extinguish a response. That means that outcome is based on effectiveness. For instance, how effective was some sleep strategy in extinguishing night wakes? Not necessarily, is sleep training harmful? It’s important to look at the theoretical framework guiding the research study as it will impact the questions and outcomes. If a similar study was done using an attachment based perspective, the study will yield different results.

Fifth, in studies that examine things like sleep, cognition, and executive functioning, the measures used aren’t necessarily developmentally appropriate given that most studies are conducted on young infants and toddlers (<3.5 years old). For instance, we know that toddlers aren’t developmentally capable of higher ordered skills, and therefore, this measure might not be telling us anything. As well, behaviour checklists are one piece of the puzzle. A clinician would use a variety of measures to determine whether or not there’s a problem with a child’s functioning (e.g., clinical interview and observation).

Sixth, there hasn’t been many studies that examines what is happening in the brain and bodies during sleep training. One small study measured cortisol levels of mothers and their babies during controlled crying. The researchers found that by day three, the babies were no longer crying. However, the babies’ cortisol levels were just as high as they had been during the first two days. In other words, they were quiet, but still showed signs of stress. Given that the babies didn’t cry, the mothers assumed that everything was fine and their cortisol levels actually decreased [1]. Now this is not a perfect study. To make it stronger, the researchers could have taken a baseline cortisol measure, implemented a control group, and increased their sample size. However, it does raise some questions that should be examined further.

Seventh, most studies don’t account for attrition bias which occurs when participants drop out of a study potentially due to intolerable effects. With respect to infant sleep research, did parents drop out because the parents couldn’t tolerate some aspect of the study? If so, how was this accounted for? Were these participants included in the analysis or excluded? How does the impact the statistical power? Confounding variables?

Finally, we don’t actually have evidence to suggest that sleep training isn’t harmful. This research doesn’t exist for many reasons. Mainly, it’s not ethical. In order to obtain a strong study on the potential harm, children would have to be randomly assigned to a control group or an experimental group where there is a possibility of harm. This likely won’t pass an ethics board. You can’t potentially harm children.

In addition, this would be a really robust study that parents may find hard to accomplish. Both, the experimental group and the control group, would have to treat their babies the exact same (e.g., feeding schedule) and have controlled for other factors like stressors in the home, socioeconomic status, and underlying sleep disruptors (e.g., teething). The only thing that would be different is the sleep training method or level of nighttime responsiveness. This just isn’t realistic.

Finally, trauma and harm is subjective and it’s not easy to measure. For instance, depression, anxiety, the ability to cope, attachment, and stress aren’t always things you can see. Yes, there are checklists and other means of assessment, but they are subjective and can take time to surface.

Overall, yes we have some research that shows that sleep intervention works. We have research that shows the importance of sleep. We even have some that suggests sleep training isn’t harmful, but do we really? What is working? What is actually happening? What would the results be using a different theoretical framework? Different questions? Different measures? More participants? If we could conduct a study that really examines whether sleep training is harmful, what would those results be? There’s a lot of answers that we don’t have and that we may never have.

On the other hand, we have research that shows the importance of responsive caregiving during the early years. We know what babies need to survive and thrive. We know that a person’s needs don’t end at night. We know what’s needed to maintain healthy relationships. We must take all of this information into consideration when we’re making choices or forming opinions. The available research, its limitations, and the gaps in the research, and apply it to our unique situation and based on our best judgment. This is evidence-based practice. Evidenced based practice is not solely adhering to research studies.

I recognize that this may further add to the confusion. It poses more questions, but that is what research is meant to do! That’s why we have to look at things in the bigger picture and decide what’s best for us.

If you’re wondering if sleep training is for you, check out this post.


  1. Middlemiss, W., Granger, D. A., Goldberg, W. A., & Nathans, L. (2012). Asynchrony of mother-infant hypothalamic-pituitary-adrenal axis activity following extinction of infant crying responses induced during the transition to sleep. Early human development88(4), 227–232.

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