Bicycle DRLs - Actually reading the paper, actually looking at the
Another thread mentions Madsen et. al., "Safety Effects of Permanent
Running Lights for Bicycles", Accident Analysis & Prevention 50 (2013) 820-829. Scharf said "Read the study," But I'm pretty sure he's read only the abstract. I downloaded the study and skimmed it a few days ago. Last night I took the time to read it in detail. Here's what I found. One might say the study is a promotion of the Reelight flashing light system, powered by magnets on wheel spokes. https://www.reelight.com/en/ Those are the lights "tested" in the study. And there are enough weirdnesses in the results to indicate that this is more a promotion than a serious study. Here are details and (warning!) data analysis. They advertized they wanted to do a study and asked who in Odense wanted to participate in a light study, luring participants by promising free lights. They got over 18000 applicants, about 10% of the population. That's the first "self-selection" clue. Those who already had sufficient lighting, those who didn't care about lights and those who simply didn't hear about this would be excluded. They used a random process to select 1845 of those people to get lights immediately and 2000 people to act as a control group, promising the controls free lights if they stayed in the study for a full year. Obviously, those who got the lights knew they had them, so there's nothing "blind" about this study. Placebo effects are certainly possible, and certainly did occur - see below. Some people dropped out in the course of the 1-year time period. 3306 completed the entire year. The study scheme echoed one "Danger! Danger!" study from Portland, in that they emailed the paricipants every two months (Portland used one month) to ask about any bike "accidents" and "injuries." This is so participants wouldn't forget any of those. It seems to me that if an "accident" or "injury" is forgettable, it should be below the radar, so to speak. But they didn't want to miss even the most minor "incident." They defined "accident" as "an incident where you are forced off your bike and/or crashed either by yourself or due to collision OR NEAR-COLLISION with others." So actually, a near miss counted as an "accident"! And I suppose "forced off you bike" could be coming to a stop and having the bike topple as you stand over it. IOW, they are exaggerating dangers, as usual. More on that later. The paper does not define "injury," but recall that the Portland paper counted _any_ injury. I assume this one did too. Broken fingernail? Injury! But the injuries were still extremely rare. Overall, there were 39672 "man-months" of bike use recorded. There was no data on number of trips by bike, km traveled or hours exposure; therefore all "rates" are "per man-month." And the numbers are very low indeed. Exactly how low is a bit difficult to tell. Examining data from three of the paper's tables and doing some minor number crunching gave three different answers for injuries per man-month. Table 6 works out to 0.00103 injuries per man-month; table 8 claims 0.00489 instead; and table 9 implies 0.00318 instead. There may be something I'm missing; but whichever is correct, all those figures are extremely low! The worst yields an average of 204 months or 17 years of riding per "injury," including (I assume) very minor and forgettable injuries. Only 41 injuries were seen by medical people, and apparently none were serious. Does that sound dangerous? Similarly, accident rates per man-month were very low - only 261 "accidents" (including near-misses!) from 39672 man-months exposure. That's less than 0.007 "accidents" per man-month, including (I assume) putting one's foot down if one drops his bike. Regarding the type of "accident": It would certainly be good to collect data on what specific type of "accident" occurred or were "prevented." But there's absolutely no mention of that in the paper. They give separate numbers for winter vs. summer, daylight vs. darkness, solo vs. "multiparty," etc. but nothing at all about whether they were cars pulling out, left crosses, right hooks, cyclists running stop signs, pedestrians jumping out, bike-bike collisions or anything else. This makes actual analysis of causes impossible. However, since "solo" accidents are listed, those must be simple falls due to skidding, running into objects or pavement defects, simply losing one's balance, etc. REELIGHTS SUPPOSEDLY PREVENTED ABOUT 25% OF SOLO CRASHES! The authors acknowledge that this is flat impossible, and evidence that the riders with the lights are cooking their reports, i.e. not reporting some accidents. The authors attempt a crude correction for this effect, but I see no justification for its accuracy - certainly not down to the three significant figure reporting of results. Still, they tried using their correction (i.e. fudge factor) to improve their results, and (bottom of page 827) said "... a result of the applied correction... has the effect that NONE OF THE ESTIMATED DIFFERENCES IN THE INCIDENCE RATES ARE [STATISTICALLY] SIGNIFICANT, the incidence rates for multiparty accidents being the only but very important exception." OK, so what's the rate of those multiparty (bike-ped, bike-bike, bike-car) "accidents" (including near misses, which are not really accidents? It's 0.00178 "accidents" per man-month. That means an average of 562 months or 47 years of riding between each of those "accidents" (including near misses). How does this relate to Scharf's and Joerg's claims that DRLs make a huge, obvious difference? As usual, the actual numbers indicate a very strong probability of bull****. And the bull**** applies to the paper's conclusions regarding Reelights' magic effectiveness as well. This paper, like so many others, emphasizes changes in extremely rare hazards. Even if Reelights or other DRLs reduce "accidents" (including near misses) from - say - once every 47 years to once every 88 years on average, which is what they claim - is it really worth yelling "Danger! Danger! Buy our lights!" Well, I suppose if you own the Reelight company, or if you get a commission by selling Chinese flashlights on your web pages, you'll say it's worth it. Less biased people probably have other opinions. Which is why, contrary to Scharf's statements, only a minuscule percentage of cyclists use daytime running lights. -- - Frank Krygowski |
Bicycle DRLs - Actually reading the paper, actually looking at
Hell, Franki-boy, your complaint is longer than the paper. And you tell us only what we know already, you hate all studies that don't blow your trumpet. When will you get a new tune (or learn to sing your old tune in tune)?
Andre Jute On Monday, July 13, 2015 at 4:53:57 PM UTC+1, Frank Krygowski wrote: Another thread mentions Madsen et. al., "Safety Effects of Permanent Running Lights for Bicycles", Accident Analysis & Prevention 50 (2013) 820-829. Scharf said "Read the study," But I'm pretty sure he's read only the abstract. I downloaded the study and skimmed it a few days ago. Last night I took the time to read it in detail. Here's what I found. One might say the study is a promotion of the Reelight flashing light system, powered by magnets on wheel spokes. https://www.reelight.com/en/ Those are the lights "tested" in the study. And there are enough weirdnesses in the results to indicate that this is more a promotion than a serious study. Here are details and (warning!) data analysis. They advertized they wanted to do a study and asked who in Odense wanted to participate in a light study, luring participants by promising free lights. They got over 18000 applicants, about 10% of the population. That's the first "self-selection" clue. Those who already had sufficient lighting, those who didn't care about lights and those who simply didn't hear about this would be excluded. They used a random process to select 1845 of those people to get lights immediately and 2000 people to act as a control group, promising the controls free lights if they stayed in the study for a full year. Obviously, those who got the lights knew they had them, so there's nothing "blind" about this study. Placebo effects are certainly possible, and certainly did occur - see below. Some people dropped out in the course of the 1-year time period. 3306 completed the entire year. The study scheme echoed one "Danger! Danger!" study from Portland, in that they emailed the paricipants every two months (Portland used one month) to ask about any bike "accidents" and "injuries." This is so participants wouldn't forget any of those. It seems to me that if an "accident" or "injury" is forgettable, it should be below the radar, so to speak. But they didn't want to miss even the most minor "incident." They defined "accident" as "an incident where you are forced off your bike and/or crashed either by yourself or due to collision OR NEAR-COLLISION with others." So actually, a near miss counted as an "accident"! And I suppose "forced off you bike" could be coming to a stop and having the bike topple as you stand over it. IOW, they are exaggerating dangers, as usual. More on that later. The paper does not define "injury," but recall that the Portland paper counted _any_ injury. I assume this one did too. Broken fingernail? Injury! But the injuries were still extremely rare. Overall, there were 39672 "man-months" of bike use recorded. There was no data on number of trips by bike, km traveled or hours exposure; therefore all "rates" are "per man-month." And the numbers are very low indeed. Exactly how low is a bit difficult to tell. Examining data from three of the paper's tables and doing some minor number crunching gave three different answers for injuries per man-month. Table 6 works out to 0.00103 injuries per man-month; table 8 claims 0.00489 instead; and table 9 implies 0.00318 instead. There may be something I'm missing; but whichever is correct, all those figures are extremely low! The worst yields an average of 204 months or 17 years of riding per "injury," including (I assume) very minor and forgettable injuries. Only 41 injuries were seen by medical people, and apparently none were serious. Does that sound dangerous? Similarly, accident rates per man-month were very low - only 261 "accidents" (including near-misses!) from 39672 man-months exposure. That's less than 0.007 "accidents" per man-month, including (I assume) putting one's foot down if one drops his bike. Regarding the type of "accident": It would certainly be good to collect data on what specific type of "accident" occurred or were "prevented." But there's absolutely no mention of that in the paper. They give separate numbers for winter vs. summer, daylight vs. darkness, solo vs. "multiparty," etc. but nothing at all about whether they were cars pulling out, left crosses, right hooks, cyclists running stop signs, pedestrians jumping out, bike-bike collisions or anything else. This makes actual analysis of causes impossible. However, since "solo" accidents are listed, those must be simple falls due to skidding, running into objects or pavement defects, simply losing one's balance, etc. REELIGHTS SUPPOSEDLY PREVENTED ABOUT 25% OF SOLO CRASHES! The authors acknowledge that this is flat impossible, and evidence that the riders with the lights are cooking their reports, i.e. not reporting some accidents. The authors attempt a crude correction for this effect, but I see no justification for its accuracy - certainly not down to the three significant figure reporting of results. Still, they tried using their correction (i.e. fudge factor) to improve their results, and (bottom of page 827) said "... a result of the applied correction... has the effect that NONE OF THE ESTIMATED DIFFERENCES IN THE INCIDENCE RATES ARE [STATISTICALLY] SIGNIFICANT, the incidence rates for multiparty accidents being the only but very important exception." OK, so what's the rate of those multiparty (bike-ped, bike-bike, bike-car) "accidents" (including near misses, which are not really accidents? It's 0.00178 "accidents" per man-month. That means an average of 562 months or 47 years of riding between each of those "accidents" (including near misses). How does this relate to Scharf's and Joerg's claims that DRLs make a huge, obvious difference? As usual, the actual numbers indicate a very strong probability of bull****. And the bull**** applies to the paper's conclusions regarding Reelights' magic effectiveness as well. This paper, like so many others, emphasizes changes in extremely rare hazards. Even if Reelights or other DRLs reduce "accidents" (including near misses) from - say - once every 47 years to once every 88 years on average, which is what they claim - is it really worth yelling "Danger! Danger! Buy our lights!" Well, I suppose if you own the Reelight company, or if you get a commission by selling Chinese flashlights on your web pages, you'll say it's worth it. Less biased people probably have other opinions. Which is why, contrary to Scharf's statements, only a minuscule percentage of cyclists use daytime running lights. -- - Frank Krygowski |
Bicycle DRLs - Actually reading the paper, actually looking at the numbers:
Frank Krygowski wrote:
:They defined "accident" as "an incident where you are forced off your :bike and/or crashed either by yourself or due to collision OR :NEAR-COLLISION with others." So actually, a near miss counted as an :"accident"! And I suppose "forced off you bike" could be coming to a :stop and having the bike topple as you stand over it. IOW, they are :exaggerating dangers, as usual. More on that later. That's a perfectly reasaonble definition. If a car pulls out in front of you, and you avoid the car, but hit the curb and crash, the car has caused an accident, even though you didn't collide with it. (That, exactly, has happened to me.) -- This is not a randomly numbered sig. |
Bicycle DRLs - Actually reading the paper, actually looking at
On 13/07/2015 2:55 PM, David Scheidt wrote:
Frank Krygowski wrote: :They defined "accident" as "an incident where you are forced off your :bike and/or crashed either by yourself or due to collision OR :NEAR-COLLISION with others." So actually, a near miss counted as an :"accident"! And I suppose "forced off you bike" could be coming to a :stop and having the bike topple as you stand over it. IOW, they are :exaggerating dangers, as usual. More on that later. That's a perfectly reasaonble definition. If a car pulls out in front of you, and you avoid the car, but hit the curb and crash, the car has caused an accident, even though you didn't collide with it. (That, exactly, has happened to me.) That has exactly happened to me too and isn't that uncommon IMO. It seems that when you have a point to prove, nothing short of death will be counted as dangerous. |
Bicycle DRLs - Actually reading the paper, actually looking at
On 7/13/2015 11:55 AM, David Scheidt wrote:
Frank Krygowski wrote: :They defined "accident" as "an incident where you are forced off your :bike and/or crashed either by yourself or due to collision OR :NEAR-COLLISION with others." So actually, a near miss counted as an :"accident"! And I suppose "forced off you bike" could be coming to a :stop and having the bike topple as you stand over it. IOW, they are :exaggerating dangers, as usual. More on that later. That's a perfectly reasaonble definition. If a car pulls out in front of you, and you avoid the car, but hit the curb and crash, the car has caused an accident, even though you didn't collide with it. (That, exactly, has happened to me.) In San Francisco I see that kind of "near miss" often, though I prefer to call it a "near hit." With a DRL the driver behavior is visibly better. You can literally see them hesitate, then yield the right of way. Does it always work? No. Today a delivery truck did a right hook in front of me in Cupertino as it turned into the Apple campus. It really wasn't a "near hit" but it was still annoying. The bottom line here is this. Frank doesn't use a DRL. Hence he believes that DRLs are ineffective. Any study that shows that belief to be false must have some terrible flaw in how it was conducted. Or change "DRL" to "helmet." The schtick is always the same. |
Bicycle DRLs - Actually reading the paper, actually looking at
On 7/13/2015 12:03 PM, Duane wrote:
On 13/07/2015 2:55 PM, David Scheidt wrote: Frank Krygowski wrote: :They defined "accident" as "an incident where you are forced off your :bike and/or crashed either by yourself or due to collision OR :NEAR-COLLISION with others." So actually, a near miss counted as an :"accident"! And I suppose "forced off you bike" could be coming to a :stop and having the bike topple as you stand over it. IOW, they are :exaggerating dangers, as usual. More on that later. That's a perfectly reasaonble definition. If a car pulls out in front of you, and you avoid the car, but hit the curb and crash, the car has caused an accident, even though you didn't collide with it. (That, exactly, has happened to me.) That has exactly happened to me too and isn't that uncommon IMO. It seems that when you have a point to prove, nothing short of death will be counted as dangerous. What I don't understand is what is the upside of the denial. Everyone is aware of the benefits of DRLs for motorcycles. Everyone is aware of why some countries mandate DRLs on cars. Is there any reason why someone would think that a study that also showed DRLs to also be effective for bicycles must somehow be so bogus that it's necessary to desperately search for some fatal flaw? No one is forcing anyone to use DRLs on their bicycle (though for motorcycles and cars they are sometimes mandatory). It's just one fairly easy way to make yourself much more conspicuous to motor vehicles in certain riding environments. In most cases the flashing DRL capability is already present in whatever lights you use at night (except for most dynamo lights) so there is no extra expense other than charging the batteries a little more often. |
Bicycle DRLs - Actually reading the paper, actually looking at
On 7/13/2015 2:55 PM, David Scheidt wrote:
Frank Krygowski wrote: :They defined "accident" as "an incident where you are forced off your :bike and/or crashed either by yourself or due to collision OR :NEAR-COLLISION with others." So actually, a near miss counted as an :"accident"! And I suppose "forced off you bike" could be coming to a :stop and having the bike topple as you stand over it. IOW, they are :exaggerating dangers, as usual. More on that later. That's a perfectly reasaonble definition. If a car pulls out in front of you, and you avoid the car, but hit the curb and crash, the car has caused an accident, even though you didn't collide with it. (That, exactly, has happened to me.) Their sentence said "...forced off your bike and/or crashed..." That "or" says that one could be forced off without crashing. If a near miss causes a dismount but no crash, is it really an accident? I have a Bike Friday, a folding bike with no top tube. That means when I stand astride the bike, it's somewhat prone to tip over because it lacks the stabilizing effect of a top tube between my legs; and it has tipped over several times that way. I would never report that as an accident. -- - Frank Krygowski |
Bicycle DRLs - Actually reading the paper, actually looking at
On 7/13/2015 2:28 PM, Andre Jute wrote:
Hell, Franki-boy, your complaint is longer than the paper. Wrong, as usual. -- - Frank Krygowski |
Bicycle DRLs - Actually reading the paper, actually looking at
On 7/13/2015 3:36 PM, sms wrote:
What I don't understand is what is the upside of the denial. Some people value accuracy and truth, whether or not you do. -- - Frank Krygowski |
Bicycle DRLs - Actually reading the paper, actually looking at
On 7/13/2015 3:29 PM, sms wrote:
The bottom line here is this. Frank doesn't use a DRL. Hence he believes that DRLs are ineffective. Any study that shows that belief to be false must have some terrible flaw in how it was conducted. Address the points I noted in the paper. I gave numbers and statements quoted from the paper, plus some further data analysis. If you see errors, why not post corrections? (Yes, I know... to do that, you'd have to actually read the paper!) The authors themselves accept that DRLs cannot possibly reduce solo accidents; yet the DRL users claimed the lights magically reduced solo accidents by 24%. The authors realized that indicated bias, and therefore they attempted a (somewhat clumsy) mathematical correction to their raw data to account for DRL users obvious bias. That takes the purported DRL benefit down to a mere 19%, and turns a negligible "accident" (not crash) rate of one per 47 years into a more negligible rate of one per 88 years of riding. What part of that did you not understand? Perhaps the fact that they observed so few instances of the problem you so greatly fear? -- - Frank Krygowski |
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