Bed sharing, in which parents sleep in the same bed with their infants, is a fairly common practice in North America and the United Kingdom. Parents who bed-share sometimes do so to facilitate breastfeeding, or because they believe it helps babies feel safe or that it will lead to closer emotional relationships.
However, many people believe that bed-sharing might be bad for children's development. And, the American Association of Pediatrics officially recommends against adults sharing a sleeping surface with infants under the age of six months because of the potential risk of sudden infant death.
A large study aimed to see if there were relationships between bed sharing and emotional and behavioral outcomes. The study was summarized by PsyPost here. The study illustrates the use of regression (Chapter 9) and is an example of a null effect (Chapter 11).
The researchers aimed to clarify whether bed-sharing during infancy has any lasting influence on a child’s development, particularly concerning emotional stability and behavioral tendencies.
The study utilized data from the Millennium Cohort Study, a large, nationally representative longitudinal study from the United Kingdom. This cohort followed over 18,000 infants born in the early 2000s, tracking their development through various stages of childhood. For this particular research, the focus was on children who were bed-sharing at 9 months of age and their subsequent emotional and behavioral development up until they were 11 years old.
a) Given the information above, what can you infer about the external validity of this study--can it generalize to the population of children in the UK?
To assess emotional and behavioral outcomes, the researchers used the Strengths and Difficulties Questionnaire, a widely respected tool for measuring psychological adjustment in children. This questionnaire, completed by parents when the children were 3, 5, 7, and 11 years old, allowed the researchers to track patterns of internalizing symptoms, such as anxiety and depression, and externalizing symptoms, like aggression and hyperactivity, over time.
b) The passage above addresses construct validity. It tells you how emotional and behavioral outcomes were measured, but it doesn't say much about whether this measure is reliable and valid. What might you want to know about this measure to decide if it is construct valid?
The study also accounted for several other factors that could influence a child’s development, including gender, socio-economic status, night-waking frequency, breastfeeding practices, maternal psychological distress, and parenting beliefs. By considering these variables, the researchers aimed to isolate the specific impact of bed-sharing on child development.
Interestingly, while bed-sharing at 9 months was more common among children in the groups with elevated symptoms [of emotional and behavioral symptoms], the researchers found no direct evidence linking bed-sharing to an increased risk of these symptoms once other factors were taken into account. In other words, after considering variables like parenting beliefs and maternal distress, bed-sharing itself did not predict whether a child would belong to one of the higher-risk groups.
c) Read the passage above and restate the simple bivariate relationship between bed-sharing and emotional/behavioral symptoms.
d) Now consider the regression analysis. What is the criterion variable?
e) What are the predictor variables? (Hint--there are seven of them)
f) Given the results described above, what might the beta have been for the bed-sharing predictor variable?
To summarize the results so far: There was a bivariate relationship between bed-sharing and symptoms. However, it seems that this bivariate relationship was attributable to some third variable like parenting beliefs or maternal distress because when these variables were controlled for, the relationship between bed-sharing and emotional/behavioral symptoms went away.
g) In Chapter 11's section on null effects, you learn that we can be more confident that null effects are real in the population when the study has more power and precision. What do you think--to what extent does this study help support that there is no relationship between bed-sharing and emotional/behavioral symptoms?
Suggested Answers to Selected Questions
b) we might want to know why the Strengths and Difficulties Questionnaire is described as "well-respected." Do parent's reports on this scale also go with other evidence of children's difficulties or psychologists' ratings?
c) The bivariate relationship is that kids who bed-shared at age 9 months had more emotional/behavioral symptoms at age 10-11.
d) The criterion variable was emotional/behavioral symptoms
e) The predictor variables were bed-sharing, gender, socio-economic status, night-waking frequency, breastfeeding practices, maternal psychological distress, and parenting beliefs.
f) The beta for bed-sharing would have been zero, or close to zero, because the text says, "after considering variables like parenting beliefs and maternal distress, bed-sharing itself did not predict whether a child would belong to one of the higher-risk groups."
g) This study's strength is its large sample of 16,000 children. Such large samples lead to more narrow 95% CIs and more precision in our estimates. If we can't find an effect of bed-sharing with this large of a sample, we probably won't find it. In other words, it would take a lot of exceptional cases to budge our "zero" conclusion. I think we can trust it.