Overall I appreciate this book SO MUCH for its sensible, nonjudgemental, and calm approach to parenting in the early years. In the intro Oster writes:
"We know being a parent means getting a lot of advice, but this advice is almost never accompanied by an explanation of *why* something is true or not, or to what degree we can even know it's true. And by not explaining why, we remove people's ability to think about these choices for themselves."
For those two sentences alone, I am pretty much willing to marry this woman.
Oster is an economist and, as the subtitle says, applies a data-centred approach to figuring out how to tackle common early parenting decisions. Major focuses include breastfeeding, sleep training, sleep and SIDS, transition to solid foods, potty training, vaccines, and child care and preschool choices.
She is explicit about her framework and how she evaluates the legitimacy and usefulness of the studies she looks at; for example, favouring studies with randomized trials and large sample sizes. She discusses major studies and interprets the data, but she never tells you that you have to take any course of action. How refreshing! She also has a fun dry sense of humor that is sprinkled throughout ("Some things about a second child are harder, the main one being the presence of the first child.")
Her approach works great for some topics: those that lend themselves to that kind of analysis she values. This means issues that have a significant medical/scientific/biological component. She shows, for example, that many claims about the health/medical benefits of breastfeeding -- such as better longterm health, IQ, and immune system for the baby -- are not supported by the data. (Lower lifetime rates of breast cancer for the breastfeeding parent are though!).
The chapter on vaccines is excellent too; Oster is careful to include information about adverse effects that are scientifically proven and their severity and rarity, and concludes that unless your kid is immune compromised, the data overwhelmingly supports early combined vaccinations.
As the book goes on into issues relevant to toddlers such as philosophies of different preschools and discipline programs, Oster's approach becomes a lot less useful. There simply isn't good data to help you make those kinds of decisions because there are too many variables. What type of preschool will be best for your kid depends on what type of kid you have.
She does share a few concepts she uses as an economist that can help with decision making on the more nebulous, which I thought were fairly useful. It's good to be reminded that you can approach emotionally loaded decisions systematically. I liked her insistence that what *you* want to do as a parent is an important factor you should consider.
In the last section, Oster begins to sound like a broken record because she keeps repeating that there is no universally relevant data on such-and-such issue, so make the decision that works best for your family. I guess this might be helpful if you were convinced you had to do a certain approach for a reason other than it was what you thought was best for your family.
If you decide to read this book -- and I do think it's overall worth it -- I'd recommend reading at least the first section before your kid is born, as it offers guidance on decisions you'd be taking into action right after childbirth -- most importantly, breastfeeding but also others like common practices in hospitals such as "rooming in" (aka the baby staying in your recovery room 24/7) and routine vitamins and antibiotics given to newborns.