A good dialogue is always fun. Thanks for bringing some science to the thread.
You've hit the nail on the proverbial head regarding misuse. Misuse is a problem across installation types: belt-only, and with Latch/Isofix. Some people get so confused they install with both methods.
Lowering misuse is a top design goal. Stated differently: we want to make things so simple that people have to work hard to make a mistake.
You are absolutely correct that belt misuse is a problem (per the cited GDV study). Latch misuse is still a problem too, though.
The studies make clear that misuse is common across installation types, to various degrees. The studies don't do a great job of exploring why the misuse occurred (The 2005 NHTSA study below did ask some good follow up questions). For example, Why did someone not use the belt path correctly? Was it because the slot was too narrow? Was it not visually obvious? Why did someone install both the Latch/Isofix anchors onto the same mount point? Why did someone leave too much slack in the Latch/Isofix anchor or the seat belt? Etcetera. The reasons why people misuse a seat are very valuable to improved public education and improved product design.
NHTSA's 2005 large field study found 39% of CRS (aka baby car seats) were incorrectly installed with Latch. Many of those had multiple errors (e.g. twisted belt plus latch connector turned upside down).
Table 11 has the details in https://www.nhtsa.gov/sites/nhtsa.gov/files/latch_report_12-...
10 years later, NHTSA's 2015 study with NCRUSS data found misuse was still persistent:
"Overall misuse is considered as having at least one defined misuse present in the car seat or booster seat – the seat may have one or multiple misuses, where one misuse has the same contribution as multiple misuses. The overall misuse is estimated to be 46 percent with a 95 percent confidence interval ranging from 39 percent to 52 percent. By car seat or booster seat type, estimated misuse rates were 61 percent for forward-facing car seats, 49 percent for rearfacing infant car seats, 44 percent for rear-facing convertible car seats, 24 percent for backless booster seats, and 16 percent for highback booster seats." Source: https://crashstats.nhtsa.dot.gov/Api/Public/ViewPublication/...
So for all those parents out there, read your seat's user manual. The user manual will make it clear how to properly and effectively use the seat belt or the Latch/Isofix anchorages.
You've hit the nail on the proverbial head regarding misuse. Misuse is a problem across installation types: belt-only, and with Latch/Isofix. Some people get so confused they install with both methods.
Lowering misuse is a top design goal. Stated differently: we want to make things so simple that people have to work hard to make a mistake.
You are absolutely correct that belt misuse is a problem (per the cited GDV study). Latch misuse is still a problem too, though.
The studies make clear that misuse is common across installation types, to various degrees. The studies don't do a great job of exploring why the misuse occurred (The 2005 NHTSA study below did ask some good follow up questions). For example, Why did someone not use the belt path correctly? Was it because the slot was too narrow? Was it not visually obvious? Why did someone install both the Latch/Isofix anchors onto the same mount point? Why did someone leave too much slack in the Latch/Isofix anchor or the seat belt? Etcetera. The reasons why people misuse a seat are very valuable to improved public education and improved product design.
NHTSA's 2005 large field study found 39% of CRS (aka baby car seats) were incorrectly installed with Latch. Many of those had multiple errors (e.g. twisted belt plus latch connector turned upside down). Table 11 has the details in https://www.nhtsa.gov/sites/nhtsa.gov/files/latch_report_12-...
10 years later, NHTSA's 2015 study with NCRUSS data found misuse was still persistent: "Overall misuse is considered as having at least one defined misuse present in the car seat or booster seat – the seat may have one or multiple misuses, where one misuse has the same contribution as multiple misuses. The overall misuse is estimated to be 46 percent with a 95 percent confidence interval ranging from 39 percent to 52 percent. By car seat or booster seat type, estimated misuse rates were 61 percent for forward-facing car seats, 49 percent for rearfacing infant car seats, 44 percent for rear-facing convertible car seats, 24 percent for backless booster seats, and 16 percent for highback booster seats." Source: https://crashstats.nhtsa.dot.gov/Api/Public/ViewPublication/...
So for all those parents out there, read your seat's user manual. The user manual will make it clear how to properly and effectively use the seat belt or the Latch/Isofix anchorages.