Drownings avoided with life jackets: model development Presentation by Dr. L. Daniel Maxim

Disclaimer Contents of brief represent potentially useful ideas—work in progress (WIP)—not necessarily a finished product The contents of this briefing have not yet been approved by competent USCG authority Your ideas welcome Written working paper available

Outline of presentation Need for valid model Model development Numerical illustration for open motorboats Parameter estimates Uncertainty The way forward

Need for model Generally accepted that life jackets can avoid drownings, but only if worn… Limited success with voluntary initiatives has prompted USCG to consider options for mandatory life jacket wear Regulatory proposals must be supported by valid analyses and may be subject to challenge

…but only if worn Many accidents involve immersion without the opportunity to don a lifejacket—or the opportunity to retrieve one from the boat! http://www.madmariner.com/seamanship/piloting/story/ ROGUE_WAVE_CLAIMS_CAPTAINS_LIFE_112210_SP.

Why care about drownings? Single largest cause of US recreational boating fatalities Drownings account for ~ 70% of US recreational boating fatalities (2008 data shown at right)

Drownings trends: slight downtrend, but still very important

Model antecedents Similar to those developed and routinely employed by NHTSA for motorcycle helmets, seat belts, and air bags Life jacket model reflects similarities and differences from helmets

Model development

Model structure: logical possibilities Number of potential drownings Wear life jacket Do not drown Drown Don’t wear life jacket

Logical possibilities: focus on wearers Number of potential drownings Wear life jacket Do not drown Drown

Logical possibilities: focus on wearers Generally accepted that lifejackets prevent drownings, so the probability of survival given immersion is enhanced Still, lifejackets do not guarantee that drownings are avoided, for reasons shown following

Why might people drown who wear a life jacket? Illustrative reasons The life jacket worn was not the right size, the right type for the sea conditions, was old, worn out, broken (e.g., malfunction of CO2 system), torn, or worn improperly The vessel capsized and the wearer was trapped inside because egress was impossible or the life jacket actually prevented egress The victim drowned from wave splash (mouth immersions) before rescue The boater received an injury or impairment that, by itself, didn't kill the boater, but was severe enough to prevent the boater from doing those things necessary to keep the boater’s face out of the water or prevent what are termed "mouth immersions" from restricting the victim’s airway over time

Improper wearing of life jacket

Improper wearing of life jacket

How captured in model Define g as probability that person who wears life jacket does not drown Therefore, 1 – g is probability that person who wears life jacket does drown Probability g difficult to estimate empirically, but presumably “relatively high” NTSB estimated that 85% of those who drowned would have survived if wearing life jacket—by this estimate, g = 0.85

Logical possibilities: non wearers Number of potential drownings Don’t wear life jacket Do not drown Drown

Why might people survive if not wearing life jacket? Reasons The boater was able to find some other object (e.g., stayed with the boat, found a life ring) that was able to be used for floatation The potentially fatal mishap occurred in an area sufficiently close to the shore that the boater was able to swim to safety The potentially fatal mishap occurred in sufficiently close proximity to one or more other vessels that they were able to rescue the potential victim Continued emphasis on swimming skills important

Survival without life jacket

How captured in model Define k as probability that person who does not wear a life jacket yet does not drown Therefore, 1 – k is probability that person who does not wear a life jacket and does drown Probability k more difficult to estimate directly, but presumably lower than g Estimation of k illustrated in later slides

Logical possibilities: focus on number of potential drownings

Number of potential drownings, F Not known, a priori But drownings result from boat occupants entering the water as a result of capsizing, falls overboard, and flooding/swamping Not all potential fatalities reported because some are rescued or are able to effect self rescue and may not be involved in reportable accident Therefore, F not measured in BARD and needs to be estimated by indirect means (see other slides)

BARD 2008 Drownings According to data from BARD in 2008, capsizing, falls overboard, and flooding or swamping, accounted for 400 (78.4%) of the 510 reported drowning fatalities

Capsizing, falls overboard, and flooding or swamping

Number of potential drownings, F Notation Number of potential drownings, F Wear life jacket Do not drown Drown Don’t wear life jacket g S1 u D1 1 - g k S2 1 - u D2 1 - k

Data BARD provides annual data on number who drowned wearing life jackets (D1) and number who drowned not wearing life jackets (D2) JSI provides data on wear rates (u) NTSB and others provide estimates of g How can these inputs be used to estimate drownings avoided?

Numerical example: open motorboats

Open motorboats—why? Drownings on open motorboats accounted for 252 (49%) of the 510 reported drownings in 2008 Including the four boat types with the highest number of reported drownings—open motorboats, canoes, rowboats, and kayaks—the total drownings in 2008 among these types were 391, 76.7% of the total drownings in that year

Sequence of calculations Number of potential drownings, F Wear life jacket Do not drown Drown Don’t wear life jacket 93.3 0.85 0.179 521.4 14 0.15

Number of potential drownings, F Filling in the blanks Number of potential drownings, F Wear life jacket Do not drown Drown Don’t wear life jacket 93.3 0.85 79 0.179 F = 521.4 14 0.15 0.449 192 0.821 236 0.551 428.1

What if: wear rate u had been higher? If u were to equal 1 (100% wear), then D1 would equal 78, and 252 – 78 = 174 drownings would be avoided Potential drownings avoided can be calculated for any assumed u Easy calculation using spreadsheet software

Uncertainty analysis of wear rate Wear rate with mandatory PFD uncertain, but likely to be less than 100% Drownings avoided at u = 0.7 (USACE estimate) ≅ 109 annually Estimate uncertain, but clearly much greater than drownings avoided under present Strategic Plan

Parameter estimates: detailed model

NTSB authoritative and applies to overall US data What about g or k? Selected estimates g k Source 0.93 NR Lunetta et al. (1998) Finland 0.90 Oregon State Marine Board 0.85 NTSB (1993) 0.75 MCA (UK) also MSA (NZ) 0.74 Browne et al. (2003) New York 0.68 0.50 Australia (1992 – 1998) 0.55 0.42 Cummings et al. (2010) 0.38 0.12 Hudson and Conway (2003) fishermen in Alaska NTSB authoritative and applies to overall US data

NTSB Study Analysis of data from 18 states; ≅ 52% of fatalities Considered 281 drownings where boater not wearing PFD Experts concluded 85% might have survived if wearing PFD Provisionally recommended for use with detailed model

The way forward

Technical Apply to multi-year data sets Apply to other types of craft (i.e., canoes, kayaks, and rowboats) Additional research on some technical issues Rewrite working paper for less technical audience? Thing to avoid—micro analysis of data

Some technical work already done Figure at left shows D1 and D2 values for open motorboats for five-year period Numbers relatively stable Use of five year averages changes estimates slightly

Some technical work already done Excluding boats with unknown length, 86.4% of 2008 drownings occurred on boats ≤ 21 ft long Therefore, focus of effort should be on smaller craft Type probably better cut than length, but correlated

Drownings “the big four”

Focus

Technical analysis: recommendations Address “big four” (open motorboats, canoes, kayaks, and rowboats) using simplest model, but focus on open motorboats Avoid further disaggregation (e.g., time of day, season) because of sample size issues Need to ensure that correct values of u are used from JSI report Preliminary answers on next slide assuming u = 0.7

Illustrative results Quantity Open Motorboat Canoe Kayak Rowboat Total Drownings Avoided Base case D1 115 34 68 10 D2 1323 340 106 214 D 1438 374 174 224 Years 6 D per year 239.7 62.3 29.0 37.3 u 0.177 0.312 0.739 0.371 New u1 0.7 New D1 456.09 76.28 18.87 New D2 481.97 148.26 102.07 New D 938.06 224.54 120.93 156.34 37.42 20.16 Drownings avoided 83.32 24.91 17.18 125.41 (34%) Illustrative results

Status Model and calculations reviewed and deemed appropriate by NTSB Work group formed to consider way forward including Dr. Linda Quan, NTSB, and Coast Guard personnel Working paper written and slight revisions made as result of input from group

Way forward This analysis preliminary and limited to “science” issues If mandatory life jacket wear to be considered, then a cost-benefit analysis will be required The benefit side of the equation obviously includes lives saved, but may include other benefits (e.g., near drownings avoided)

Way forward Proposed regulation needs to be justified using content and format in accord with OMB Circular A-4 (among other things) Other issues need to be addressed, e.g., What are likely compliance rates? Need to limit potential lives saved to “waters subject to the jurisdiction of the United States” What costs are appropriate to include?

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