COMBINING RISKSFROM TWO LEADING FACTORS IN STAIR-RELATED FALLS
Jake Pauls1 and Ben Barkow2
1

Jake Pauls Consulting Services, Silver Spring, Maryland, USA
and 2207-255 Glenlake Avenue, Toronto, Ontario, M6P 1G2 Canada
2
Behavioural Team, 75 Kenwood Avenue, Toronto, Ontario, M6C 2S1 Canada
and Delray Beach, Florida, USA
Two key aspects of stairway step geometry are nominal dimensions of step rise andrun (also known as “going”) plus the uniformity of those dimensions. A survey of
UK home step dimensions found a risk range of 0.02 to 0.10 “accidents” per year,
varying inversely with runs from about 250 to 195 mm. An inverse relationship,with more variables documented, was found in earlier research in a UK laboratory
with a wider range of step runs, 280 to 190 mm, as used generally in buildings.
Other research identified non-uniformity of step run and/or rise as a potent risk
factor with risk ratios estimated in one or more orders of magnitude (i.e., factors of
10). A newly identified research challenge is to determine what the overall risks
are—for a large set of stairs—when both nominal step geometry and uniformity
are jointly implicated in falls. This improves understanding of how national fallinjury data might be distorted by faulty nominal and non-uniform step dimensions.

Introduction
Stairs are a major site for injurious falls whether in occupational settings, where there can be
relatively good control of most risk factors, or homes, where there is little control of risk factors
including those resulting from significantly lower standards for design, construction and use plus
their regulation. In the USA there are relatively good national statistics, including stair-related
injuries treated in hospital emergency departments, from the US Consumer Product Safety
Commission (CPSC) National Electronic Injury Surveillance System (NEISS). Annual national
estimates, which can be tabulated by treatment, setting, victim age, etc., are freely available on theInternet (CPSC/NEISS, 2013). Using NEISS data, analyses have been done of thedisproportionate occurrence—and relatively rapid recent growth—of more-serious, stair-related
injuries in home settings, relative to all others (Pauls, 2011).
Important environmental factors in stair-related falls have been identified over the last few
decades. During this time, and in several countries, the role of step geometry has gained growing
prominence. Selected highlights of this prominence include studies by researchers, in the USA,e.g., Alessi, et al. (1978), Archea, et al. (1979), Templer (1984, 1992), Hay and Barkow (1985),
Cohen, et al. (2009); in Japan, by Kose, et al. (1985), Nagata (1985), Nagata and Kim (2007); andin the UK by Roys (2001), Roys and Wright (2005), Wright and Roys (2005, 2008). Other
research findings include work by Johnson and Pauls (2010) and Pauls (2011). (A 20-page list ofliterature providing primary, secondary and tertiary treatments of stairway safety/risk factors, andassociated controls including safety codes and standards, is available from the lead author.)Complementing such historical studies is extended research, for example, in major laboratories
studying falls: Japan NIOSH, US NIOSH, UK HSL, Liberty Mutual Research Institute for Safety
in the US, and, in Canada, the Toronto Rehab Institute iDAPT research centre—responsible forthe best website on stair usability and safety research plus technology (TRI iDAPT, 2013). It is
fortunate to find that physical aspects of stair construction are implicated in injuries. These aspects
can be accurately measured and produced in construction and remediated after the fact of a fall.

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Early estimates of stair-related injury risks

Generally, risk is described as the ratio of some outcome relative to a unit of exposure. One of
the early estimates of stair-related risk was published by Archea, et al. (1979). The outcome
measures ranged from minor missteps (defined as departures from normal gait) through to death,per stair flight use. Flight use is a meaningful measure of a user’s encounter with a stair flight(sometimes referred to simply a flight, defined, like stair, as a single series of steps), Risks of a
misstep are highest within one, two, or three steps of the transition from level walking to stairwalking and in the transition from the other end of the flight in transitioning to level walking.
Table 1 provides these estimates—based on very early NEISS data—for the year 1975. The
terminology used is exactly that used in the 1979 report. The third column, derived from thesecond column, was added in Table 1 to make the estimates of Archea, et al. more useful.
Table 1. Risk estimates for US by Archea, et al. (1979)———————————————————————————————————
Incident type
Incidents/year
Risk per flight use———————————————————————————————————
Flight uses
1,953,000,000,000
1.0———————————————————————————————————
Noticeable missteps
264,000,000
1 / 7,400
Minor Accidents
31,000,000
1 / 63,000
Disabling Accidents
2,660,000
1 / 734,000
Hospital Treatment
540,000
1 / 3,617,000
Related Deaths
3,800
1 / 513,947,000———————————————————————————————————

Updating early estimates of stair-related injury risks

If Table 1 were revised for conditions in the US based on NEISS national data for 2012, it
would be relatively definitive at 1,297,930 for all stair-related hospital emergency department
visits (growing by a 2.4 multiple). After correcting for population growth (215,973,199 to
313,933,954), this would still represent a large increase—by a multiple of 1.65. Rates per
100,000 population were respectively 250 and 413 for emergency department visits in 1975 and2012. The 2012 rate for 78,876 stair-related hospitalized cases was 25.1 per 100,000 population.
Obtaining an estimate of flight uses for 2012 is problematic; the 1975 estimates by Archea,
et al. were based on about 25 flight uses per day per person in the USA. Given many lifestyleand other changes over the intervening 37 years, we would estimate a somewhat lower per
capita use of stair flights, say 20 flight uses per day. Aging of the population during this interval
is a separate trend that may need to be taken into account. However, in calculating risk, this canbe accounted for in estimating exposure, by lowering it accordingly.
Therefore, the 2012 risk is about one hospital emergency room visit (“Hospital Treatment”
in Table 1) for every 1,766,000 flight uses, a doubling of the risk in the intervening 37 years.
Analysis by Pauls (2011) supports a doubling of the risk based on analysis of stair-related
hospital-admission cases with more comparable data for the period, 1997-2009: “In the 12-year
period, age-adjusted rates (per 100,000 population) of such injuries grew 103 percent (3.8 to7.7) for people <65 years of age; 85 percent (36.9 to 68.1) for people ≥65 years of age.”As shown in Pauls’ (2011) analysis of the NEISS data from 1974 to 2009, there wasrelatively modest growth of stair-related injuries in the US until 1997. Between 1997 and 2009,
the ratio of all estimated US emergency department visits (and to some extent for hospital
admissions) for home settings versus all other known settings grew from about 5-to-1 (the ratio
between 1975 and 1997) to about 10-to-1 in 2009.

Utility of information for stair-related injury risks

In the foregoing discussion there are two different metrics used to describe risk; one typical of
traffic and other safety professionals based on incidents per exposure (i.e., kilometers, hours ofuse), the other based on incidents per population per year. The other is more typical of publichealth epidemiology professionals, the source of much of the admittedly limited information- 88 -

about the risk of falls and the even more limited information about how and why falls occur. If
there were no material changes in stair usage (“exposure”) over time, the epidemiolgicalapproach and the safety approach should track one another.
A dramatic change began about 1997 in the relative risks of stair use in US homes versus
stair use elsewhere in the US. Much of the impetus for this paper is to help make a case forresearch to determine how and why this happened in the US (and possibly elsewhere, including
Canada). Our hypothesis is that the combinations of risks for these settings changed, partly due
to the differences in both nominal step geometries and the uniformity of such geometries.
For example, “Top Of Flight Flaw” (TOFF), is a disturbingly pervasive, systemic nonuniformity defect in home stairs in the US and Canada, as described by Johnson and Pauls(2010). TOFF is a candidate, partial explanation for what is happening with risk of stair use.
TOFF incidence exacerbates safety if occurring with other step dimension defects; for example,
systematic TOFF might be accompanied by random non-uniformities in step geometry. Bothcomplicate the risks coming from systemically smaller (nominal) step runs (going) in homes.
Non-uniformities, have a large impact on observable missteps on stairs as well as risk ofserious injuries. Johnson and Pauls (2010) estimate impacts in orders of magnitude (factors often). Also, forensics-based insights have repeatedly shown that non-uniformities are often
implicated as proximate causes for missteps and falls (e.g., Cohen, et al., 2009).
Publications from the last decade and especially, conference presentations provide
important insights from UK studies into the effect of differences in nominal step size,
particularly the run (going) dimensions (Wright and Roys, 2005, 2008). As shown in Figure 1,
this work, using both objective and subjective measures in laboratory and field survey work,suggests that nominal step geometry, notably the run (going) dimensions can impact actual andperceived safety by a multiple of 7 (as much as 11 for residential-type carpet covering which
reduces effective tread run to as little as 190 mm). These multiples could be a key part of theanswer along with the order-of-magnitude estimates of non-uniformity effects noted above.

Figure 1. Graph combining results from a subjective measure of stair safety
in a laboratory study with results from a survey of home step dimensions
and experience with “accidents” on the stair (Wright and Roys, 2005, 2008)

Combined risks of different nominal step run or going dimensions
with varying incidence of top-of-flight non-uniformities
Table 2, below, is a illustrative result of combining two risks. This is acceptable to the degree of
which they can be considered as acting independently, linearly, and are otherwise numericallywell-behaved. Not included here is a table showing results if those simplifying assumptions
cannot be sustained (e.g., with dependent factors that require mulitiplication). An example of- 89 -

dependent probabilities occurs if the misstep in a TOFF situation is more difficult to mitigate
due to generally short tread runs, e.g., 210 mm, permitted in Canadian homes.
Table 2. Estimated relative annual risks per 100,000 population, of US hospital emergency
department visits for home stair-related falls with various nominal run (going) dimensions
and with various occurrences of Top of Flight Flaw (TOFF) non-uniformity
Uniformity
condition:
Percentage
of stairswith TOFF
0
2
5
10
15
20
25
30
35
40
45
50
55
60

Annual injurious fall risk rates with various nominal tread runs
Risk rates shown are per 100,0000 population
190 mm
210 mm
230 mm
250 mm
280 mmEffective run
Used in codes
Favoured by
Minimum in
Minimum inwith carpet
in Canada
US home
ICC codes
NFPA codesbuilders

230
250
260
290
320 (10 x Ref)
350
380
410
440
470
500
530
560
590

140
150
170
200
230
260
290
320 (10 x Ref)
350
380
410
440
470
500

110
120
140
170
200
230
260
290
320 (10 x Ref)
350
380
410
440
470

50
62
80
110
140
170
200
230
260
209
320 (10 x Ref)
350
380
410

20
32 (Ref)
50
80
110
140
170
200
230
260
290
320 (10 x Ref)
350
380

Relative risks as affected by nominal step geometry come from Figure 1, based on studies
by Wright and Roys (2005, 2008). Increased risk posed by TOFF is conservatively assumed to
be a factor of 30, based on observations by Pauls as reported in Johnson and Pauls (2010).
The 10 times criterion (“10 x Ref”) is based on what has been documented for the entire US
during the period 1997 to 2009, with home stairs responsible, by 2009, for about ten times as
many hospital emergency department treatments as those for all other known settings. (Recall
that this was compared with a multiple of only five in the 23 years during which NEISS data
were collected before 1997.) In Table 2, the cell, “32 (Ref),” for 280 mm run combined with 2
percent incidence of TOFF, applies to US non-home stairs associated with 32 emergency
department visits, per 100,000 population, for stair-related injuries during 2012.
Risks shown in Table 2, described using the surrogate measure of emergency department
visits per 100,000 population, are hypothetical based on a few assumptions derived from thework of a few leading researchers into stair safety over a period 1975 to 2008 (specificallyArchea, et al, plus Wright and Roys, 2005, 2008, along with conference presentations by thelatter). Contributing to the amalgam of such diverse studies is the judgment of the lead author ofthis paper, using these inputs to develop first-order—or better—estimates of risk, expressed inunits widely used in public health. These can compared with epidemiology data such as NEISS
national estimates of stair related injuries in 2012 resulting, in hospital emergency department
visits—at an annual rate of about 413 per 100,000 population.
It should be clear that Table 2 represents theory-based estimates to spur further research andanalysis. These estimates are therefore superior to first-order estimates and relate most closely
to US data. The authors intend that the relative risks inform the Canadian home stair safety
situation with its code-permitted, 210 mm runs and evidence of much non-uniform construction.
Not included in Table 2 is the near worst-case scenario with every stair having nonuniformities due to TOFF (at the top of stair flights) or randomly located ones. These would
result in estimates of about 600 to 800 per 100,000 population for the step geometries arrayed
across the table. The logical end-point would be the combination of both systemic and random- 90 -

non-uniformities plus very short tread runs. Sadly, such a prospect cannot be dismissed if
competencies in home construction and its inspection continue an apparent downward trend.
In Table 1, relationships among missteps and falls (from Archea, et al., 1979) have beenused to re-characterize the two-year “accident” survey results of Wright and Roys (2008). Bothsources used the term “accident” to describe falls, but failed to be specific about severity orconsequence. For example, Archea, et al., used the designation “disabling accidents” todescribe incidents that led to the need for some minor medical attention (i.e., either in home orin a doctor’s office, urgent care center or hospital) not long-term disability.
Using injury epidemiology, we now know that, in the US, for every visit to a hospital, there
are about 1.5 professional medical treatments in other settings. From this we could estimate that,for every hospital emergency department visit, there are on the order of four other treatments,
either within the home or undocumented in another treatment setting. This results in a ratio of
about 5-to-1 between what Archea, et al. termed “disabling accidents” and “hospital treatments”(their estimates being, respectively, 2,660,000 and 540,000, a ratio of 4.93-to-1, for the year
1975 in the US). With significant changes in healthcare delivery, there are and will bedifficulties using the foregoing assumptions in future analyses of risk.

Discussion
Along with firearms and tobacco, stairs are among the most dangerous product we utilize in ourhomes in terms of public health costs, particularly relative to costs of manufacture orconstruction or remediation. While less recognized as being an aspect of public health, usability
is also a major area where stairs, especially in our homes, exact huge costs comparable to oreven greater than, the injury costs. Comprehensive, societal injury costs estimated by Lawrence,
et al., (1999) were on the order of five million dollars per hour in the US for 1995. With recent
growth in injury costs, the current estimate is about 10-million dollars per hour in the US.
Inevitably, stair behaviour is influenced by the perception of risk (Hay and Barkow, 1985).
After all, there are no falls until a user takes their first step. The perceptions of risk held by users
are most veridical and hence lead to the safest outcomes when grounded in factors known to berisky from objective studies such as those summarized in this article.
In Hay and Barkow (1985) the user rankings of stairs were compared to actual fall data andto expert opinion. Naïve users, it was found, are not naïve about risks because their ranking of
40 stairs correlated r=.78 with a panel of recognized experts and r=.28 with the cost of injuries.
So it is useful to relate factors empirically known to be risky such as TOFF to the degree inwhich users perceive them as risky. Moreover, as part of a comprehensive program of stairsafety, users need education in stair defect identification, e.g., TOFF (Johnson and Pauls, 2010).
Regarding research, and other public health measures to better understand how stair-relatedrisks can be assessed and managed or mitigated, if not eliminated, we need:• Improved epidemiological data collection, analysis, interpretation and publication.
• Surveys of homes (and other buildings) to determine the incidence of, and factors
determining, the actual dimensions of steps of stairs, taking into account nominal values
as well as non-uniformities, their types, sizes, locations and conspicuity.
• Studies of adaptations people employ to detect and mitigate non-uniformities.
• Programs to educate designers, builders, regulators and others about stair risk reduction.
What information is held by ergonomists and safety experts, for example, that is notcommunicated and worse, is not applied. How many inspectors, for example, know how
to do the “crouch-and-sight test,” that takes no more than ten seconds to perform? Yet itis effective and should be tried at the start of an inspection (Johnson and Pauls, 2010).
• Information on stair hazards needs to be communicated to users so as to make theirperceptions of risk veridical—accurate and meaningful—as they begin their first step.
The foregoing list is incomplete and the reader, having gotten this far into this paper, will
have thought of much more. Like two other papers submitted by the lead author to ICFPP2013(and prior conferences in this series, e.g., Pauls, 2007, dealing with misstep typology), theobjective is not only to spur badly needed new research but to improve our ability now to- 91 -

identify and discuss the key issues using more specific terminology than, for example, “minor
accidents.” Stairways—the term used to describe not only the steps but also the handrails andother features of stairs—have long fascinated a wide range of people for technical as well as
many other reasons. They clearly warrant our careful attention, and much more.

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