The methods devised to 'sleep train' babies vary widely, however, they can be thought of as falling broadly into two groups:
- Methods designed to treat existing 'sleep problems': These include 'extinction' methods (more commonly known as Cry-It-Out and Controlled Crying), and are designed to prevent a baby being 'rewarded' with parents' attention for crying whilst settling to sleep, or on waking during the night. Other methods which fall into this category include Scheduled Awakenings, and 'Gradual Withdrawal'.
- Methods designed to prevent 'sleep problems' from developing: These focus on development of routines or schedules which are broadly designed to help babies differentiate between night-time as sleep time, and day-time as wake, play and feed time.
In addition to the above many sleep training methods include Parent Education - whereby parents are provided with information about infant sleep patterns, crying, and ways to prevent or tackle existing sleep problems.
Reviews of the sleep training literature show that the majority of published studies (over 80%) report positive outcomes, regardless of what method is being tested, with the greatest amount of support (in terms of number and quality of studies) existing for 'extinction' methods. By 'positive' we mean that the research studies achieved one or more of the goals aimed for. In most cases these goals included outcomes such as an increase in the amount of sleep mothers reported for their babies or themselves, a decrease in the number of times babies woke during the night, or a beneficial effect on a variety of other outcomes including mothers' depression and children's day-time behaviour. Some studies found that the improvement seen in mothers' or babies' sleep was only significant for part of the group who took part. Hiscock & Wake (2002), for example, conducted a large randomised trial of controlled-crying/camping out, with 8-10 months old babies. They found that the overall improvement seen in the number of mothers reporting infant sleep problems two months later was due to significant improvement occurring only in the sub-group of participants that included depressed mothers. There was no significant improvement in the 'non-depressed' group.
Although the vast majority of studies have reported initial increases in infant sleep duration, and/or reduction in night waking, relatively few studies have investigated whether this effect persists long-term. Of the studies that have addressed this issue (only 3 - one quarter of the publications we included in our systematic review for this summary) none found an effect lasting 6 months or more after the sleep training method was originally used, and found to 'improve' babies sleep. This means that the initial improvement, or benefit of using the method disappeared, and outcomes were the same for the group of babies who had been sleep trained as for those in the control group who had not.
Limitations of the research
Although the high percentage of published studies reporting 'positive' results is impressive, these figures alone do not tell the whole story. One of the biggest problems with evaluating this body of research is the huge variety in the way studies were conducted, and what they aimed to achieve. Some of this variation includes:
- Who takes part in the research: babies involved in the studies we reviewed for this summary ranged in age from 0-45 months, and included families with newborns (and hence no 'sleep problems'), to families needing 'some help' with their baby's sleep, to families reporting severe and ongoing sleep disruption.
- How sleep training methods are implemented, including what methods are used: not only are there a wide range of techniques, from Cry It Out to 'positive bedtime routines' and 'parental education', often more than one method is used within one study, making it hard to disentangle what works from what has no effect.
In addition to these variations, studies can be very different in terms of design:
- Some are large randomised controlled trials that often have the benefit of large sample sizes, and participants are randomly allocated in an attempt to isolate the effects of the method being used, but also tend to need to use low-cost, easily collected data (such as parental reports) due to the huge numbers of participants;
- Others are very small controlled or non-controlled trials that don't have the benefits of large-scale RCTs but can often use costly but objective data-collection methods such as video observation or sleep monitoring devices.
- Some studies attempt to alter the way babies sleep, or the way mothers sleep, or on other sleep-related issues such as mother or child mental and physical health, and family relationships.
For these reasons, few studies that have been done are directly comparable to others, and those that are comparable tend to be done by the same research team, using similar groups of participants. Drawing conclusions about the effects of using sleep training methods in one group of individuals based on studies done on another - quite different - group, is therefore extremely difficult.
We also need to be aware that for some participants, simply taking part in a research project can change the way they act, or think about their infants' sleep. One study, that looked at parents' experiences of taking part in a sleep training intervention, found that being in the project made some participants feel more determined to implement aspects of the method - including controlled crying - than they would otherwise have been, thus making the method more successful in changing their babies' sleep as part of a research trial than they would have been if they were using the method alone without taking part in a research project. In another study, parents surveyed by Loutzenhiser et al. (2014) remarked upon the difficulty they had implementing techniques within the home versus in the clinical or research setting. The reality being that many techniques were more stressful on both parents and infants than initially anticipated.
Finally, we know that the vast majority of publications reporting on tests of sleep training methods produce 'positive' results -- this raises the question of whether studies that produce negative results get published at all. How many studies have examined sleep training methods that haven't worked? We have no way of knowing!
Overall, there is good evidence that sleep training methods can change (parental reports of their) babies' sleep patterns in the short term. What is less clear is how this happens, and what other -- unintended -- consequences of such training might be. We consider these issues in the following page.