Phase II - Safety-Enhancing Motor Vehicle Child Safety Seat
Conditions: Motor Vehicle Injury, Safety Issues
Sponsor: Minnesota HealthSolutions

Version: 5/2024 
 
 
Official Title: Phase II - Safety-Enhancing Motor Vehicle Child Safety 
Seat 
NCT Number: NCT06384989    
Document Date: May 2024 
Document Contents: Study Protocol and Statistical Analysis Plan 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

Version: 5/2024 
Study Protocol and Statistical Analysis Plan 
Background 
Engineers from our Small Business partner, Minnesota HealthSolutions, have designed a new prototype 
child car safety seat. The car seat includes a load leg, which is a relatively new feature that braces the base 
of the car seat against the floor of the vehicle. The load leg helps to absorb crash forces and prevent 
movement of the car seat and its occupant during a crash. Load legs already exist on a few car seat 
models on the market today, but Minnesota Health Solutions has created a new design that absorbs energy 
in a novel way.  
The research team from the Ohio State University (OSU) was involved in a Phase I SBIR with the 
prototype car seat. In that project, the prototype was shown to 15 volunteer participants (12 caregivers and 
3 certified Child Passenger Safety Technicians (CPSTs)). The study participants practiced installing the 
car seat and gave verbal and written feedback on the understandability and ease-of-use of the load leg. 
They provided information about their families’ travel habits and whether they saw value in the newly 
designed feature. 
In this Phase II SBIR proposal, OSU will conduct additional human subjects testing to gauge the usability 
of the new car seat safety feature in a more in-depth and quantitative approach. 
Objectives 
The primary objective is to assess the usability of the load leg design for caregivers who must install the 
child safety seat into a vehicle. The specific aims are to quantify any errors committed by the participants 
while installing the car seat and to assess participants’ opinions on the car seat’s load leg design. 
Research design 
A descriptive study will be conducted to determine whether human subjects are able to install the new 
feature of the prototype car seat correctly. Participants will be presented with the prototype car seat and a 
set of basic written instructions and labels to guide their installations. The percentage of participants who 
use the new feature and use it correctly will be reported. Any installation errors on other parts of the child 
seat (seat belt, lower anchors, top tether) will also be reported. 
Detailed study procedures 
Recruitment 
Announcements will be posted in OSU employee newsletters, volunteer mailing lists, department mailing 
lists, and social media. Interested participants will be asked to email the study team. Study personnel will 
send a response email to determine if the participant is eligible to participate.  Pre-screen questions will 
identify potential participants who meet the following criteria: 
1. Age 18 or older 
2. Be a care provider to a child who is up to 2 years of age 
3. Have installed a child safety seat in the last 2 years   
4. Able to lift and install a child safety seat into a vehicle 
5. English-speaking 
Participants who meet the above criteria will be asked to schedule an individual appointment. 

Version: 5/2024 
Enrollment 
Participants will be enrolled for one 30 minute time slot. Upon arrival at the scheduled time, participants 
will be briefed on the study protocol, sign the IRB approved consent form, incentive payment receipt, and 
will be given the incentive payment.   
Session Protocol 
Each participant will complete the consent process and sign the consent form. The participant will be 
asked to install the prototype car seat into a vehicle. A basic set of written instructions and labels on the 
car seat will be provided. The researcher will explain that they cannot answer any questions during the 
installation and that the participant may take as long as needed. If a participant completes the installation 
without using the load leg, this outcome will be noted and then the participant will be prompted to re-
install the child seat using the load leg. When each installation is completed, the participant will be led 
away from the vehicle while a researcher evaluates their work. A researcher who is a CPST will use a 
data collection form to keep track of all installation errors committed by the participants. The primary 
outcomes of interest are the rate of load leg installation (without being prompted to use this feature) and 
correct installation of the load leg. Other errors of interest include routing of the seat belt or lower anchor 
straps, looseness of attachment, recline angle, etc.  A handheld tension gauge will be used to quantify 
installation tightness. All other metrics are a visual pass/fail metric. 
Following the installations, participants will complete a short survey with open-ended queries to describe 
facilitators or barriers they experienced while installing the seat, as well as what they liked or did not like 
about the seat. They will use a Likert scale to rate their self-efficacy in installing the seats, if they 
believed they were installed correctly, and general ease-of-use. Socio-demographic data will also be 
collected (e.g. gender, age, and socioeconomic status). After study procedures are completed, the 
researcher will demonstrate how to correctly install the seat and provide the participant with educational 
materials.   
Internal/external validity 
Product usability studies are an effective, low-risk way to obtain information about a product design. 
Published work exists as a model for product usability protocols (for example: Mirman et al. 2015, 
Mansfield et al. 2018). Product usability studies help to highlight consumer habits and attitudes which 
engineers and product designers may not be aware of.  
Data/statistical analysis 
The percentage of participants who install with the load leg (without being prompted) will be recorded. 
Any installation errors associated with the load leg will also be recorded. Other errors will also be 
recorded as a percentage of the study sample (belt routing, looseness of attachment, etc.). The rates of 
these common errors will be compared to those reported in recent literature. There are currently no 
resources reporting typical error rates for load legs since this feature is not widely available in the current 
car seat market. The proposed study will provide a benchmark for this factor. Any installation errors with 
respect to the load leg will be analyzed for their likelihood of causing potential harm to the occupant.  
The participant information collected in the surveys will be analyzed using descriptive and inferential 
statistics. Descriptive statistics such as means, standard deviations, medians, ranges, and frequency 
distributions will be calculated from the Likert scale data according to type of safety seat. Continuous 
data will be checked for normality. We will use either paired t-tests or Wilcoxon signed-rank test for 
correlated data to test the hypothesis of no change on ratings of ease-of-use and self-efficacy. Logistic 
regression will be used to predict correct load leg usage (pass/fail) using perceived self-efficacy, gender, 
and age of participants for each device.  

Version: 5/2024 
Bibliography 
 
Mansfield JA, Zaragoza-Rivera YN, Bolte JB IV. Usability of non-standard lower anchor configurations 
for child restraint system (CRS) installation. Traffic Injury Prevention. [Accepted 21 Oct 2018, release 
pending editor’s formatting] 
 
Mirman JH, Seifert SJ, Zonfrillo MR, Metzger K, Durbin DR, Arbogast KB. Evaluating the effect of a 
mechanical adjunct to improve the installation of child restraint systems to vehicles. Traffic Injury 
Prevention. 2015; 16(sup2):S24-S31.