UK research

British researchers (Families, Children and Child Care (FCCC)) conducted a longitudinal study of the care of 1,201 UK children from birth to school age, recruiting mothers between 1998 and 2001.

"At the time of the 1201 three-month interviews, 101 mothers were using non-maternal child care for 12 hours per week or more. A further 426 mothers who were not yet using non-maternal care indicated that they soon would be (total 527), however, follow-up telephone enquiries established that only 304 of them were actually using at least 12 hours of any form of non-maternal care by the time their infants were seven months old (total 405) and 198 of these infants did not reach the appropriate age for this sub-study before the end of the time period during which the specialist child psychiatry registrars were available to conduct interviews. Accordingly 207 of the 405 mothers (51.1%) took part in the “early child care” study."

..."To assess whether these 207 mothers differed from the pool of 405 from which they came, a series of group comparisons was conducted on factors found to be related to child care."

"...Overall, compared with those eligible, those who took part in the ‘early child care’ sub-study include fewer of the best educated, fewer of those with the highest incomes, and fewer of the most ‘progressive’ mothers." [View source]

Leach, Penelope; Barnes, Jacqueline; Nichols, Michelle1; Goldin, Jon; Stein, Alan; Sylva, Kathy; Malmberg, Lars-Erik and the FCCC team, "Child care before 6 months of age: a qualitative study of mothers’ decisions and feelings about employment and non-maternal care", Infant and Child Development, 2006, 15:471–502.