What Does a 30% Chance of Rain Mean? (Understanding Risk, with Gerd Gigerenzer) | Big Think

[@CaptnDeadpool]

It means that out of 100 hypothetical scenarios of today's weather, in 30 of those scenarios it's gonna rain.

[@cubedude76]

i still want to know what 30% chance of rain means

[@Caarnji]

You find rain probability expressed as a percentage mostly on the internet and on news and it´s not really what the meteorologist deal with, just to represent it understandably (without mile-long charts). If you look at such a forecast it mostly is about a place and time-span (mostly city/day) and is simply how likely in that timespan in that place it is to rain, not sure what the big mystery is there^^

[@NikomaGrob]

***** The big mystery is life.

[@clintgirard677]

***** ur gonna be constipated lol and tired. u gotta sleep and shit too.

[@MilesMartinez]

It's 30% of the region. Hank had a meteorologist as a host on SciShow Talk Show one time and that's what he said it was! :)

[@Caarnji]

***** It´s not 30% of the region, that´s one factor though, the other is if precipitation will occur, based on many things from the meteorological present data and holding it against past data of the region. To have the probability of rain in a a place you need both, the percentage doesn´t say that in 30% of a city it will rain, it tells the probability in that city to encounter rain (the maths of course needs also the area, since fraction of cloudage and windspeed is a big factor for giving a chance of rain for a region). It seems he told that they use coverage in the equation for determining the chance and you interpreted it meaning the final probability given just means coverage, not sure didn´t saw that show. :p

[@ParaditeRs]

30% chance of rain means that there is a 30% chance that it might rain at a given time. I have never met anyone who has seen it as anything other than that and I have lived in 9 states.

[@sd4dfg2]

You mean per given minute? So the odds of raining at least once in an hour are 1-(0.7^60), or 99.999999949%? Or did you mean any given second? You did exactly what he said in the video.

[@ParaditeRs]

sd4dfg2 Given time as in the time frame given with the forecast. I guess I wasn't clear.

[@P8Dealer]

You must be kidding :D

[@2ftpmarco]

What does 30% rain mean? Well, you have to figure that out yourself. Yeah.......and it means 100% -1 vote for bigthink.

[@IXOY3007]

I always thought, along with everyone I know, that 30% chance of rain meant that there is a 30% chance that it will rain at some point in the day. And there is a 70% it won't rain at all that day. I have never heard of it being anything else.

[@maillolhelloworld737]

There are a varieties of solutions to deal with risk, but the utmost important thing is that you should know how to deal with your own problem yourself. Knowing the cause of risk and the assumption of experts can help to figure out what you concern and take action. Thanks for sharing.

[@HexerPsy]

What does 30% rain mean? Well, you have to figure that out yourself. Yeah...

[@Lello991]

+HexerPsy What meteorologists intend to say is that it will rain on 30 percent of the days for which this prediction is made (Gigerenzer G., Risk savvy, How to make good decisions, Viking Adult, 2014)

[@HexerPsy]

Alessandro Ansani So he did actually say it in the video, but with lacking emphasis... However, that definition doesnt agree with other definition found out there: www.srh.noaa.gov/ffc/?n=pop PoP=C*A Probability of Precipitation is Confidence (that percipitation will occur somewhere in the forecast area) times Area (that will receive measurable precipitation, usually more than 0.25mm). Its rounded off in steps of 10%. It has nothing to do with days - a rainstorm may miss the area and fly over elsewhere. This uncertainty drags down the chance. In addition, if it will only rain part of the area, this will drag down the probability as well... While you could summarize the formula in his statement, i find it rather inaccurate and misleading. Because a high percentage means: we are fairly sure a large area will receive measurable rain. And a low percentage could mean several things: Either 1) we are fairly unsure that a large area will get measurable rain. Or 2) We are fairly sure a small area will get rain. Or 3) something in that spectrum between those extremes. However, my original statement still stands... What does 30% chance of rain mean? He never gives a proper answer or explanation behind how the weather models arrive at that figure.

[@Iionios]

It seems there's alot of misunderstanding here, what Dr. Gigerenzer is trying to say is the need for reasoning when dealing with risk prevention. If the experts can't, or won't, communicate the meaning of a percentage directly, we need to ask the experts for more details. "Percent chance of what, exactly?" With research you can learn that 30% chance of rain is a forecast saying "3 of 10 meteorologists say it will rain". But unless you actaully search for this information, as a consumer, you will never be told.

[@SebastianSkadisson]

that's exactly it, being aware that percentage and mere statistics can never be the whole truth to go with. if stock exchange speculators would go only for the pure numbers and calculated chances they would be out of the game very fast.

[@Caarnji]

"With research you can learn that 30% chance of rain is a forecast saying "3 of 10 meteorologists say it will rain"." Bad research, would be totally wrong. lol You think forecasts indicate date+place for no reason? The likeliness of rain ALWAYS are for the indicated place and time given and the likeliness of that rain occurring in that place at that time based on METEOROLOGICAL DATA like humidity, temp, wind and not counting what which meteorologists say. lmao^^ I find it funny that people take anecdotes from a guy talking on YT as research, or where did you get your "facts" from? :p "we need to ask the experts for more details. "Percent chance of what, exactly?"" Aehm...in that case it´s the likeliness of rain for INDICATED time and place... , which fundamental information would be missing?

[@Caarnji]

Sebastian Skadisson Or they may not crash economies, useless scumbags should be replaced by computers dealing with probabilities, I bet my right ass cheek it turns out better. Of course you would need to find them real jobs, which is a tiny problem.

[@victornpb]

Never ever thought that this was not obvious... chance is chance, it is not distribution over a territory, or distribution over period of time. chance is having it or not. like there's 30% of chance of me getting a cake today. i'm not going to get 30% of a full cake or eating 30% of the cake during a time period. either you have it or not, and the probability is saying probably not. duh

[@Caarnji]

***** Jep, otherwise 100% rain would be what...a tsunami or the pacific ocean coming down? lol Think people are confusing probability of rain in those forecasts with being intensity or other factors ..so of course if they think that they might get confused with this data. :p

[@Pectusx3]

Nahh i live in germany too and ive never heard of somebody who misinterpreted the chance of rain like this...

[@RhamonGB]

Yeah, me neither, and I live in Brazil

[@MacDKB]

Obviously, it means there is a 3 in 10 chance that it will rain. Is it true that most people don't understand this? _Really_? Well, it explains a lot. In fact, I have noticed that anything under 50% almost always means it won't rain. And only when it reaches 60% can you be sure there will be rain...

[@AtomicRooster190]

Another part of what 30% chance of rain means is that computer models indicate there's a 30% chance of rain occurring in that FORECAST AREA. Those areas are LARGE. So if there's a shower in a small part of the forecast area, but in 95% of that area there was no rain at all, then the meteorologists weight the event with 100% certainty that rain did occur. This is why forecasts seem to cry wolf. The forecasts are not designed to be digested by an individual who occupies a point in a forecast area. Forecast percentages only make sense to people with Doppler radar.

[@seonteeaika]

I think it's 30% chance that it rains *at least once* during given time frame, say "afternoon" which would mean several hours. It doesn't account at all on how much it could rain, or how many small rain clouds could randomly pass by. Additionally you could say that to define "rain", certain amount of water during the time frame would need to drop. So in that sense it does affect a little on how much it could rain.

[@TheUnchainedMind]

I find people's interpretation of a "30% chance of rain" to be puzzling. To me it's just that, that there is a one in three chances of rain.

[@cockerrocker]

Do you know what it means?

[@TheUnchainedMind]

cockerrocker It means that based on scientific data, there is a one in three chances of rain for whatever time interval concerned by the forecast. This is an abstract prediction. Asking "what it (really) means" is completely pointless. If I wanted to know more about the natural processes at work, I'd study them, and learn how such conclusions have been reached.

[@cockerrocker]

How is the question pointless? I've asked plenty of people and they don't know or they think it means there's about a 1 in 3 chance that it will rain. The percentage is based on two variables, the chance that precipitation will form, and the coverage of the precipitation that will form.

[@yousuckmorethanido]

how much rain? when? where...

[@TheUnchainedMind]

cockerrocker I'm saying that nobody (read: most people) gives a flying fuck about the intricacies of weather forecast. What we're talking about is understanding the meaning of the percentage. Believing that it means it will rain during 30% of the time is, in my opinion quite outrageous. I'm expressing my puzzlement at people failing to comprehend something as simple as this. What lies beneath the prediction, as interesting as it might be, is completely irrelevant to this point,

[@Dyslexic-Artist-Theory-on-Time]

This is like understanding the statistics risk of nuclear accident!!! Think for your self!!!

[@andrewthecelt3794]

I can't believe there's confusion about this. I don't agree that the problem lies with meteorologist, seems like the issue is an ignorant public. From NOAA: When the National Weather Service (NWS) refers to PoPs, we are referring to the Probability of Precipitation. This is the likelihood, expressed as a percent, of measurable precipitation (≥ 0.01 inch) at a particular point during a specified time period. In other words, if you learn that the NWS is advertising a 60% chance of rain for your specific location, then out of 100 days with the same atmospheric ingredients in place, we believe it will rain on 60 out of those 100 days (or a 60% chance). When we advertise a chance of rain for a daytime period, it ranges from 6 am to 6 pm (6 pm to 6 am for nighttime periods). Link to full page with more detail: www.srh.noaa.gov/jax/?n=probability_of_precipitation

[@itsbobfoster]

With respect to your example about a percentage probability of rain, I thought about the three main variations in meaning some time ago and called the national weather service in my country, which is Canada. When I posed the question and the three examples of possible meanings, the person answering my question was honest enough to say that he really didn't know what it meant. I would suggest that there is another dimension here and that is deciding what constitutes rain. If I go outside and single drop falls on my head, but I see no other rain for the entire day, did the probability when the drop hit me change to 100%?

[@misterpurplesky]

'30% chance of rain' means: if you care 30% about being dry and comfy, take an umbrella

[@hdpasd123lol]

Just to get this straight. 30% chance of rain, means that for example if we had 10 days with the same conditions as the day in question, it would rain in 3 out of the 10 days right? That is what i understand.

[@jordonsoper9483]

I may be wrong but doesn't 30% chance of rain mean that if that exact day were to occur 100 times (with identical weather conditions based on those meteorological predictions) on thirty of those days it would rain regardless of how much, how long or where it would rain on those days?

[@clintgirard677]

if u cant get past the fact that u still dont know what 30% means, then u missed the entire point.

[@adnanilyas6368]

30% chance of rain tomorrow? Where I live, that means we will have snow tomorrow.

[@NikomaGrob]

Hahaha that cracked me up, thanks.

[@shadk89]

Where I live, it means time to build an ark.

[@withoutwithin]

Where I live, that means it's summer.

[@NCbassfishing24]

A 30% chance of rain means that 30% of the area that the forecast applies to will receive rain during the allotted time period that the forecast applies.

[@TheBluMeeny]

30% chance to rain in your area, since weather patterns are always shifting, meteorologists can't know exactly where it will rain, it is a 30% chance where there instruments indicate there is a storm.

[@ramcannon]

Lol I used to think it meant the intensity of rain. 30% would mean that you would have slight rain.

[@Caarnji]

Mostly forecasts also forecast the intensity, what did you think the intensity meant? :p

[@erdwaenor]

The conclusion may sound obvious, but it's actually fascinating.

[@BeeChomper]

So 30% chance of rain means it is 70% likely that not a single drop of rain will fall in that time period. Say that prediction was made for a 1 hour period and that prediction held for every hour in a given day (12 hours), the likelihood that no rain will fall on that day would be 1.4% right? So in essence if you were planning a day out to the beach you can forget it, but if you only wanted to take your dog for a walk or go park and play frisbee then its happy days right? (since the chance of it raining every hour of the day would be basically 0%) This is of course assuming the weather prediction is valid all the way from your house to the beach

[@alanmead9830]

It's funny, he never mentions that there is a correct answer to the 30% question; the "NYC perspective" is the correct one. I guess that's a good example; I recall a friend complaining about 50% chance of rain, "Why don't they just tell us if it will rain?" she complained because (Gigerenzer's point) she didn't certainly did not understand risk. But this little talk is unhelpful. It's like he's lecturing people walking down train tracks that they "don't understand trains." It would be nice if he gave us a few pointers like "Listen for the train." or "Don't walk on train tracks." And I grant you that understanding risk and making good decisions is a hard task but psychologists and other have been documenting the heuristics and biases for decades and explaining those, even one of them, would be of genuine benefit. I suppose it's unfair to compare books to 4-minute videos but I found more value in reading Richard Posner or Nicholas Taleb -- they explain why people do things like text and drive. In fact, my guess is that the folks who get the most out of this talk are other psychologists who study decision making under uncertainty.

[@JustSumChillAlien]

What if it meant 30% chance on a certain hour/hours. Because if you have an iOS device, & you go on the weather app, it has %'s on the hours shown the chance of rain on those hours. I'm not sure if Android devices have a weather app like that, that shows you %'s on the hours line of that day if it says it was going to rain or not.

[@Lowmandavis]

30% chance of rain means there is a chance Of rain, only 30% chance it will rain at all that day and 70% chance it won't rain at all that day

[@UWBadgers10]

A weather forecast is a prediction made by meteorologists using collected data e.g. wind speed, direction, humidity, temperature etc. To me it is 30% chance that the forecast is correct given the data they use for their prediction. If it actually is raining, they can predict it with 100% confidence.

[@Caarnji]

Nope, it´s simply the chance you get wet in a particular place in a particular time-span (which any forecast indicates, otherwise it´s a pretty bad forecast lol). Has nothing to do with the prediction of the data, the prediction is of the likeliness of rain due to what you said above (and even 100% rain probablity for a city won´t mean you have to get wet, since it varies in cities too, while the prediction is totally correct and for 100% it will rain in that city, you still can be somewhere in that city where it doesn´t rain)

[@CreatorsAbout]

I've always thought 30% chance meant a low chance clouds will blow my way. Raining for 30% percent of the day just sounds absurd. How are you to know what the chances of that happening is?

[@HighscoreBoy]

30% CHANCE of rain means its a 30% CHANCE it might rain, key word here is chance

[@P8Dealer]

You must be kidding :D

[@741iop741iop]

BUT WHAT'S THE SAMPLE SPACE?!?!?! ...moments in time? ...points on a map? ...meteorologists (or more likely, whether models)? I wan't to know!

[@TheAssassin409]

weatherman, the only job where you can be 100% wrong 100% of the time and still keep your job

[@RigalicReign]

30%-100% rain, I still gotta work in the rain so I just deal with it...

[@Mjp74]

I look at it like like there's a 70% chance that's its going to be a rain free day or dose it really matter?

[@Chamelionroses]

Even if taught to speak or listen there are those that will assume what they want instead f seek understanding. Culture and language... one can not fix stupid or just those that choose to be ignorant.

[@spacedoubt15]

Well thanks for clearing that meteorology thing up.

[@JeffsterRocks]

This is stuff is taught in the primary school...

[@1hanEEn1]

His accent is fucking awesome

[@FlStudioFreakForLife]

I kind of already had this figured out. I knew that the only reason why doctors become doctors is because of things other people have taught them, not because they have a mind of a god who can tell the future on whether or not you live or die. I know some of you would be confused with that sentence but it's my perspective. Lol. It makes sense to me so yeah.

[@imthetank3]

right, cause they are learning what others have learned. There can be a totally difference approach that yields better results, but until someone figures that method out, no one can learn it.

[@michaelirwin6137]

He didnt even answer his own damn question

[@TheXxkornmunkyx666]

I don't know anybody who thinks 30% rain means that.

[@baba7231]

Is it just me ... this guy can put me to sleep

[@squirreljester2]

I still don't know what 30% chance of rain means.

[@Lello991]

+squirreljester2 · I noticed that everybody wants to know what's the exact meaning of that 30%, well, I've just read his last book (the title is "Risk savvy, how to make good decisions") and here's the answer: · "What meteorologists intend to say is that it will rain on 30 percent of the days for which this prediction is made. And “rain” refers to any amount above some tiny threshold, such as 0.01 inches.5 Left on their own, peopleintuitively fill in a reference class that makes sense to them, such as how many hours, where, or how heavily it rains. More imaginative minds will come up with others still. As one woman in New York said, “I know what 30 percent means: Three meteorologists think it will rain, and seven not.”

[@justinosborne5280]

Where I live, if there's a 30% chance of rain, really you have a 70% chance that it will rain! It's really bullshit. 30% should actually mean 30%! Damn it!

[@Lowmandavis]

This is interesting

[@Xoid97]

sooo... what's does it really mean ?

[@whereeveritgoes]

30% chance of meatballs.

[@OfficialRedTeamReview]

I'm sorry but....what the fuck?

[@tubester4567]

30% chance of rain means the weather guy has no fucking idea but hes gonna throw some numbers out there so people think he actually studied the weather.

[@melatiro5]

wasted 4:10 minutes of my life

[@Ibokulus]

So what does 30% chance of rain mean? Did I miss that?

[@TurningString]

What?

[@DHP666BG]

can't resist.........first!

[@gaminghoot7020]

Nope, Big Think was first.

[@millionsteve]

The camera movements in this video make it difficult to watch. Thumbs down.

[@loganpierz811]

If his statistics are correct the entire planet needs to go back to school... But I don't know anyone who thinks the way he says people do

[@scottseptember1992]

WTF!?! It's videos like these that piss me the hell off. Still don't know what 30% chance of rain means. #fuckcliffhangers

[@sd4dfg2]

It means nothing, that was his point - they aren't telling you jack because they left out important facts.

[@sakisgw3]

He should speak more clear...

[@MegaMissfitz]

just to let u know theres a 30% chance i might not be able to make it today im afraid 👍👎👍

[@SuperBhavanishankar]

in mother russia, the rain will predict you!

[@jfreak18]

This is fucking depressing

[@clappic]

Obviously obvious , thank u for wastin 4 min of my time

[@McSmacks]

I still don't know what a 30% chance of rain means.

[@Procrastinerd]

Could there possibly be a more boring title to this video? How un-engaging can one get?

[@Parralyzed]

Fits the content.

[@Procrastinerd]

Parralyzed I know! Paralyzing, right?!

[@AdonisOuranios]

I actually clicked on the video because it asked this question, and I don't normally watch Big Think. Because I started thinking, "Well, what DOES it mean?"

[@Procrastinerd]

***** lol so edgy

[@Procrastinerd]

***** I didn't watch the entire video. You give me too much credit.