Interesting. I like the notation and the histogram that comes out with the output. I also like the practical examples you gave (e.g. the application of the calculator to business and marketing cases). I will try it out with simple estimates in my marketing campaigns.
Show HN: Unsure Calculator – back-of-a-napkin probabilistic calculator
101–110 of 170 posts
Re: Show HN: Unsure Calculator – back-of-a-napkin probabilistic calculator
#102”Without further knowledge, the calculator cannot know that a negative number is impossible (in other words, you can't have -5 civilizations, for example).”
Not true. If there are no negative terms, the equation cannot have negative values.
Re: Show HN: Unsure Calculator – back-of-a-napkin probabilistic calculator
#103On the whole it seems like a nice idea, but there's a couple of weird things, such as:
> Note: If you're curious why there is a negative number (-5) in the histogram, that's just an inevitable downside of the simplicity of the Unsure Calculator. Without further knowledge, the calculator cannot know that a negative number is impossible (in other words, you can't have -5 civilizations, for example).
The input to this was "1.5~3 x 0.9~1.0 x 0.1~0.4 x 0.1~1.0 x 0.1~1.0 x 0.1~0.2 x 304~10000" - every single range was positive, so regardless of what this represents, it should be impossible to get a negative result.
I guess this is a consequence of "I am not sure about the exact number here, but I am 95% sure it's somewhere in this range" so it's actually considering values outside of the specified range. In this case, 10% either side of all the ranges is positive except the large "304~10000".
Trying with a simpler example: "1~2 x 1~2" produces "1.3~3.4" as a result, even though "1~4" seems more intuitive. I assume this is because the confidence of 1 or 4 is now only 90% if 1~2 was at 95%, but it still feels off.
I wonder if the 95% thing actually makes sense, but I'm not especially good at stats, certainly not enough to be sure how viable this kind of calculator is with a tighter range. But just personally, I'd expect "1~2" to mean "I'm obviously not 100% sure, or else I wouldn't be using this calculator, but for this experiment assume that the range is definitely within 1~2, I just don't know where exactly".
Re: Show HN: Unsure Calculator – back-of-a-napkin probabilistic calculator
#104Earlier quoted context omitted.
It is producing a useful number. As more truly independent terms are added, error grows with the square root while the point estimation grows linearly. In the aggregate, the error makes up less of the point estimation. This is the reason Fermi estimation works. You can test people on it, and almost universally they get more accurate with this method. If you got less certain of the result in the example, that's probab…
> People are default overconfident with their estimated error bars. You say this but yet roughly in a top level comment mentions people keep their error bars too close.
Sorry, my comment was phrased confusingly.
Being overconfident with error bars means placing them too close to the point estimation, i.e. the error bars are too narrow.
Re: Show HN: Unsure Calculator – back-of-a-napkin probabilistic calculator
#105I like this! In the grand HN tradition of being triggered by a word in the post and going off on a not-quite-but-basically-totally-tangential rant: There’s (at least) three areas here that are footguns with these kinds of calculations: 1) 95% is usually a lot wider than people think - people take 95% as “I’m pretty sure it’s this,” whereas it’s really closer to “it’d be really surprising if it were not this” - by and…
I did a project with non-technical stakeholders modeling likely completion dates for a big GANTT chart. Business stakeholders wanted probabilistic task completion times because some of the tasks were new and impractical to quantify with fixed times. Stakeholders really liked specifying work times as t_i ~ PERT(min, mode, max) because it mimics their thinking and handles typical real-world asymmetrical distributions.…
This looks like a much more sophisticated version of PERT than I have seen used. When people around me have claimed to use PERT, they have just added together all the small numbers, all the middle numbers, and all the big numbers. That results in a distribution that is too extreme in both lower and upper bound.
Re: Show HN: Unsure Calculator – back-of-a-napkin probabilistic calculator
#106On the whole it seems like a nice idea, but there's a couple of weird things, such as: > Note: If you're curious why there is a negative number (-5) in the histogram, that's just an inevitable downside of the simplicity of the Unsure Calculator. Without further knowledge, the calculator cannot know that a negative number is impossible (in other words, you can't have -5 civilizations, for example). The input to this w…
The calculator in Emacs has support for what it is you request, which it calls "interval forms". Interval form arithmetic simply means executing the operations in parallel on both ends of the interval.
It also has support for "error forms" which is close to what the calculator in OP uses. That takes a little more sophistication than just performing operations on the lower and upper number in parallel. In particular, the given points don't represent actual endpoints on a distribution, but rather low and high probability events. Things more or less likely than those can happen, it's just rare.
> I'm not especially good at stats
It shows! All the things you complain about make perfect sense given a little more background knowledge.
Re: Show HN: Unsure Calculator – back-of-a-napkin probabilistic calculator
#107”Without further knowledge, the calculator cannot know that a negative number is impossible (in other words, you can't have -5 civilizations, for example).” Not true. If there are no negative terms, the equation cannot have negative values.
The calculator cannot know whether there are no negative terms. For example, if people's net worth is distributed 0.2–400, there's likely a significant chunk of people who are, on the whole, in debt. These will be represented as a negative term, even though their distribution was characterised by positive numbers.
Re: Show HN: Unsure Calculator – back-of-a-napkin probabilistic calculator
#108”Without further knowledge, the calculator cannot know that a negative number is impossible (in other words, you can't have -5 civilizations, for example).” Not true. If there are no negative terms, the equation cannot have negative values.
The range notation indicates 95% confidence intervals, not the minima and maxima. If the lower bounds are close enough to zero (and the interval is large enough), then there may some residual probability mass associated with negative values of the variable.
Re: Show HN: Unsure Calculator – back-of-a-napkin probabilistic calculator
#109similar to guesstimate, which does the same but for spreadsheets: https://www.getguesstimate.com/
Re: Show HN: Unsure Calculator – back-of-a-napkin probabilistic calculator
#110Cool. It would be great to extend with a confidence operator. Something like:
Without default confidence: 0~9
With confidence: 0%100~9%95
We are sure it is 0 or more and we are %95 certain it is 9 or less.
Would that work?