While this study is relatively recent and therefore less likely to suffer from a historical bias it does however use a biased sample in that it only used predominantly middle-class and therefore it lacks external validity because it is not a representative sample meaning that findings cannot be generalised to all children in day care. Furthermore it should be noted that this research used a natural-experimental method and such a method can never establish that it is simply attending day care that caused the negative effect on cognitive development but could well be the quality of day care as the following study reveals.
Whitebook, Howes, & Phillips (1989) (National Child Care Staffing Study) carried out a study involving 227 day care centres for High, middle, and low Socio-economic status families. In total 1,309 teachers/staff were interviewed, and 260 children’s cognitive development was assessed using a number of techniques (e.g. the Early Childhood Environmental Rating Scale and Infant/Toddler Environmental Rating Scale). Findings showed that there was a significant positive correlation between quality of day care and children’s’ cognitive development irrelevant of the socio-economic status the day care was providing for. Thus it appears that it is not simply attending day care that causes negative effects on cognitive development as Vandell & Corasaniti’s research suggests but is, in fact, the quality of the day care. This finding therefore challenges Bowlby’s maternal deprivation hypothesis.
This study also has a number of other advantages over Vandell & Corasaniti’s study because unlike their study this involved a large sample of both children and day care centres and it includes High, middle, and low Socio-economic status families and thus increases its external validity. Nevertheless this sample is only representative of one culture and therefore the findings cannot be generalised to different cultures.
Furthermore there is evidence to show that day care may wll have positive effects on cognitive development, for example:
Anderson (1989) carried out a longitudinal study involving a sample of more than 100 children from a variety of backgrounds, including single parent families. The children were selected at age 3 to 4 and the type of day care recorded, together with the age at which day care was begun. The children were assessed at ages 8 and 13. They were given a range of tests of their cognitive (i.e. IQ tests, school performance) and social development (mainly teacher ratings). The findings of the study showed an association between age of entry into day care and cognitive development. That is those children who had spent longest in day care had better school performance than those who had only a short time in day care or those who were cared for at home. Consequently this shows the positive effects of day care on cognitive development.
Nevertheless there may well be a very important confounding variable in this study in that those children who started day care earliest tended to come from the wealthiest families. Thus the reason they showed superior cognitive development may well be because they came from advantaged families and not because they have spent more time in day care.
Furthermore it is also important to note that the study was conducted in Sweden, a country with a very highly developed system of social welfare, where the quality of day care is extremely high, and therefore the results may not be typical. Other studies, particularly in the US have shown different results as can be seen above.
However further support for the positive effects of day care on cognitive development has been found, for example research carried out by Caughy, DiPietro, & Strobino (1994). They studied 867 children from the National Longitudinal Survey of Youth (464 boys) comprising of 47% non-Black/non-Hispanic; 34% Black; 19% Hispanic children who has attended day care during the first 3 years of life. They compared these with a matched sample of children who had not attended day care during the first 3 years of life. The children were aged 5 to 6 years when their cognitive development was measured using psychometric tests (e.g. the Peabody Individual Achievement Test). Findings showed that children from “impoverished home environments” attending day care during the first 3 years of life scored higher on cognitive tests than those who did not attend day care. Furthermore the effects on reading scores were greatest for children who began day care before the age of 1. This shows that the effects of day care on cognitive development are positive. This finding further implies that it may well not be day care per se that is the cause of the negative or positive effects on cognitive development but is an impoverished of enriched environment that causes effects on cognitive development.
