fboulnois 2022-06-26

Many infant and child car seats are available on Amazon, but which are truly safe? The National Highway Traffic Safety Administration has a Car Seat Finder tool but unfortunately it is difficult to compare and contrast car seats across brands, features, and ratings.

To investigate in more detail I downloaded the raw NHTSA car seat data and analyzed it using R. I was also interested in highly rated car seats that are part of travel systems. These travel systems usually have a stroller and infant car seat combo but these seats are almost never convertible / multifunction. I cross-referenced the seat model of the most popular travel systems with the NHTSA data.

The car seat data was analyzed in a few different dimensions:

• Which car seats have the highest combined rating by geometric score
• Which convertible (multifunction) car seats have the highest score
• Which convertible car seats have an overall rating of 5 in any category
• Which travel system car seats have the highest score

A few organizations also perform independent testing of car seats that meet or exceed the NHTSA standards:

• BabyGearLab
• Consumer Reports

To keep this section short, the code which downloads and cleans the data has been hidden, however it can be viewed as part of the raw .Rmd file that produced this analysis.

Concisely, the NHTSA has a child seat API which returns JSON. Because that JSON has a highly nested structure it is expanded into separate rows. To help with the analysis, a few columns of data are added and some columns are reordered.

To avoid having to download the data every time, the data is loaded from a file if it exists otherwise it downloads the data from the API.

url <- "https://api.nhtsa.gov/childSeats?offset=0&max=100&sort=make&order=asc&data=modes&dataSet=ratings"
json <- "car-seat-results.json"

raw <- modify_cols(expand(load_from_cache(json, url)))

The NHTSA rates car seats across several categories:

raw[, unique(modes.ratings.type)]

## [1] "OverallRating"               "SecuringChild"              
## [3] "EvaluationLabels"            "VehicleInstallationFeatures"
## [5] "EvaluationOfInstructions"

For each rating category, the seats are given numerical values from 1 to 5 where 5 corresponds to 5 stars (i.e. the highest / best rating):

raw[, range(modes.ratings.rating, na.rm = TRUE)]

## [1] 1 5

Powerful transformations are easy to do once the data is in a data.table format. Since each rating category is different and could have different ranges, the geometric mean is used to calculate a single global average score for each car seat instead of the arithmetic mean. The OverallRating column is also used in this calculation as it does not seem to be an average of the other ratings but is instead the NHTSA reviewer’s overall rating of the car seat. Next, the table is converted from long to wide format to pull out the ratings into their own columns, the rows are ordered by highest geometric score first, and a final csv file is created.

raw[, geom.score := exp(mean(log(modes.ratings.rating))), by = id]

dt <- dcast(raw, id + modes.mode + ... ~ modes.ratings.type, value.var = "modes.ratings.rating")
setorder(dt, -geom.score, na.last = TRUE)

csv <- "car-seat-results.csv"
fwrite(dt, csv)

The ratings are mainly clustered around a score of 3.29, with some below average ratings and only a few high ratings.

The highest rated car seats in all categories by geometric score are as follows:

res <- dt[geom.score > 4.5, .(make, productModel, seatType, geom.score)]

The brands GB, Doona, Cybex, Britax, and Graco top the list of the highest rated car seats.

The highest rated convertible car seats by geometric scores are as follows:

res <- unique(dt[modes.count == 3 & geom.score > 3.5, .(make, productModel, seatType, geom.score)])

Some of the most popular convertible car seats appear in this list, including the 4Ever DLX and Grows4Me by Graco, the One4Life by Britax, the City View by Baby Jogger, and the EveryStage by EvenFlo.

The highest rated convertible car seats with an overall rating of 5 in at least one category are as follows:

res <- dt[modes.count == 3 & OverallRating == 5, .(make, productModel, seatType, geom.score)]

The Graco 4Ever DLX, Britax One4Life Clicktight, and Evenflo EveryFit top the list for highest 5-star rated convertible car seats.

I manually compiled a list of the most popular travel systems and their car seats from a couple of review sites and Amazon:

Next this table is combined with the NHTSA data to get a final list of the highest scoring travel system car seats:

res <- merge(dt, tt, by.x = c("make", "productModel"), by.y = c("brand", "seat.name"))
res <- res[, .(make, travel.system, productModel, seatType, geom.score)]
setorder(res, -geom.score, na.last = TRUE)

Unsurprisingly, all of these travel systems only have infant car seats. The three highest scoring travel systems are the Britax B-Free & B-Safe Gen 2 travel system, the Doona Car Seat & Stroller, and the Baby Jogger City Mini GT2 with the City Go 2 car seat.

Many infant and child seats are available for purchase, but only a few are highly rated by the NHTSA individually, as a convertible car seat, and as part of a travel system.

All of the data used in the analysis is available in this repository. The raw data is stored in car-seat-results.json, and the final data is stored in car-seat-results.csv.

Hopefully this analysis helps your family make the right decision!