1

General Science / Stats question: who's most likely to be at fault?

« on: 16/06/2022 17:22:28 »

Referring to this page, there are 3782 cyclists at fault for failing to look properly, and 7565 non-cyclists. If we assume that there are 8 times as many non-cycling road users as cyclists, does it follow that:

1.   Cyclists are four times more likely to be at fault because they’re producing half as many incidents from 8 times fewer vehicles.
2.   Cyclists are 16 times less likely to be at fault because non-cyclists are still producing twice the incidents despite having 8 times fewer potential targets for careless road users to collide with.
3.   From the product of 1&2 above, cyclists are four times less likely to be at fault overall.
4.   Cyclists are just half as likely to be at fault, because those who haven’t crashed are not relevant.
5.   None of the above.

Personally, I’m inclined to think it’s (3), because the probability of an accident must be the probability of finding a careless road user multiplied by the probability of them finding something to hit.

2

COVID-19 / Deaths vs Vaccination Rate

« on: 23/11/2021 15:20:45 »

This seems interesting. I'm assuming that a high proportion of African deaths are going unrecorded, and that African countries without the resources to collect death stats also have fewer resources to administer vaccines.

Vaccine temp.png (8.79 kB . 481x287 - viewed 1129 times)
https://ourworldindata.org/coronavirus

3

Physiology & Medicine / Why do brain tumours (and blood clots) cause headaches.......

« on: 16/08/2021 18:15:51 »

.....if there are no pain receptors in the brain?

I've found this:

"The headaches are not caused directly by the tumour itself, as the brain has no pain receptors, but by a build-up of pressure on pain-sensitive blood vessels and nerves within the brain."

So what's a "pain-sensitive nerve within the brain" if it's not a pain receptor?

https://www.thebraintumourcharity.org/brain-tumour-signs-symptoms/adult-brain-tumour-symptoms/headaches/#:~:text=Headaches%20are%20one%20of%20the%20most%20common%20symptoms,pain-sensitive%20blood%20vessels%20and%20nerves%20within%20the%20brain.

4

Physiology & Medicine / Anaesthetics - what's the difference?

« on: 23/07/2021 12:15:56 »

One anaesthetic: injected into the arm, count down 10 9 8 7.....gone.
Another: injection in the arm, remain awake for several minutes, then a mask on, inhale a solvent smelling gas for several more minutes, then gone.

What's the difference here, because according to the record they're both sevoflurane?

5

Just Chat! / The Gas Man Cometh

« on: 10/06/2021 18:00:08 »

There's a gas leak on the main road near here, they've only been trying to find it for the last 15 months.

They came out in March last year and stayed until June, then they were back July - September, then Nov/Dec, then January - March. By that time it looked like they'd finally fixed it, but I've just walked past this afternoon, and they're back again.

As far as I can tell, the nub of their problem is that the gas would appear to be leaking into the BT cable duct, and then by the time it's travelled for hundreds of yards up & down the duct, it's effectively disguised the location of the leak. They started poking sniffer probes down boreholes drilled in the road, then digging holes looking for it, then after a few months they seemed to be just speculatively replacing sections of pipe and waiting to see what happens.

They could have renewed the main along the whole street in all the time they've been there.

6

COVID-19 / Can we get herd immunity?

« on: 24/05/2021 13:25:27 »

So can the vaccine give us herd immunity if enough of the population have it, or will the virus continue to circulate anyway until a vaccine-resistant mutant emerges?

7

Physiology & Medicine / How much use is pulse oximetry?

« on: 26/03/2021 14:51:07 »

Since covid made pulse oximeters toy of the moment, the published advice seems to be:

>=95%: You're fine.
92% - 95%: ask your doctor for advice.
<92%: Call 999.

So from this, it would appear that the higher the oxygen saturation the better, IE there's no 'optimum', nor any homeostasis striving to achieve it.

Of the pulse oximeters on the consumer market, it would appear that the accuracy of most, if not all, is ±2%, but professional machines don't seem to quote any accuracy at all in the specifications. So if your SpO2 were 93.5% for example, your course of action upon checking it with a pulse oximeter would be either do nothing at all or call an ambulance, depending only on whether your instrument lays at the top or bottom of its tolerance range.

I have a pair of oximeters, both the same model, and the difference between them is 1.16%, based on an average of 80 pairs of readings, which is well within tolerance, but the instantaneous difference between any one pair of readings is ±6%, so you might reasonably wonder whether they're of any use at all.

My own SpO2 is all over the shop, varying from 88% to 98%, but usually 93%. If I make an effort to breathe more deeply it will rise to 95%, but if I continue it then falls back to 93%, which rather seems to suggest that there's some sort of homeostasis at work. If I breathe hard enough for long enough it makes me go dizzy, which also suggests that more isn't necessarily better.

Any thoughts?

8

That CAN'T be true! / Can this microwave boiler heat your home?

« on: 16/03/2021 16:40:16 »

There's a company here wanting to take £3500 of your hard earned cash for a revolutionary new central heating boiler that uses a magnetron to heat the water. They're claiming 96% efficiency, a wonderful improvement on the mere 100% efficiency to be had from a much more expensive and complicated resistor immersed in the water.

https://www.theguardian.com/environment/2021/mar/16/first-microwave-powered-home-boiler-could-help-cut-emissions

9

COVID-19 / Pfizer Side Effects, but what's the denominator?

« on: 16/02/2021 15:37:38 »

20,000 reports of 60,000 side effects, and 143 deaths, but no denominator.
https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/960150/COVID-19_mRNA_Pfizer_BioNTech_vaccine_analysis_print.pdf
Anyone know how many people have had a Pfizer vaccine?

10

Physiology & Medicine / CT Scanner Operation

« on: 12/02/2021 14:53:37 »

Is it possible to get a CT scan of the head with the patient table stationary, and not traversing through the scanner? How long does a head scan typically take.

11

Just Chat! / Questions pertaining to Notifications on TheNakedScientists.

« on: 04/01/2021 12:32:42 »

Questions pertaining to Notifications on TheNakedScientists

12

Technology / Anyone noticed the variability in Freeview audio?

« on: 22/12/2020 21:25:57 »

Has anyone else noticed how the bandwidth of Freeview audio keeps varying from one mic to another?

The recent Panorama documentary on the development of the vaccine would be a case in point, Fergal Walsh would be sat interviewing someone, and whilst the mic of the interviewee was crisp, sharp and sibilant, Walsh's mic was woolly, muffled and lacking in any HF response. By comparison, Walsh's commentary dubbed over the program was clear and sharp.

I'm not just talking about one program, it's a common problem. Two news presenters in a studio for example, one with a clear mic, the other muffled. Absurd, but it makes it look like half the microphones in the BBC are faulty whilst nobody has noticed.

13

COVID-19 / Are we testing the wrong people for coronavirus infection?

« on: 22/05/2020 14:46:39 »

If you're not a key worker but have symptoms, you can apply for a test (https://www.nhs.uk/conditions/coronavirus-covid-19/testing-for-coronavirus/ask-for-a-test-to-check-if-you-have-coronavirus/), but if you're already symptomatic that's reason enough to isolate, the people we need to find are the asymptomatic ones. According to the stats on the news, 40% of those in care homes are positive, and 50% of those are asymptomatic. Among staff, 80% of those infected are asymptomatic.

14

Physiology & Medicine / AF, Anticoagulation, Stroke, Haemorrhage

« on: 20/05/2020 18:20:01 »

AF risks blood clots, clots cause strokes, anticoagulants reduce the risk of clots but increase the risk of haemorrhage.

CHA2DS2-VASc estimates the risk of additional ischaemic strokes incurred by AF patients, and HASBLED estimates the increased risk of haemorrhagic strokes to patients taking anticoagulants. So, from the data in the NICE guidelines, it's possible to tabulate the net risk of stroke for each combination of Chads & Hasbled (below).


Nice Anticoag.JPG (53.64 kB . 682x407 - viewed 3364 times)

Both NICE and ESC guidelines seem inline with this:

NICE clinical guideline 180: Atrial fibrillation: the management of atrial fibrillation
"1.5.2 Consider anticoagulation for men with a CHA2DS2-VASc score of 1. Take the
bleeding risk into account.

1.5.3 Offer anticoagulation to people with a CHA2DS2-VASc score of 2 or above,
taking bleeding risk into account."

2016 ESC Guidelines for the management of atrial Fibrillation
"9.1.1 In general, patients without clinical stroke risk factors do not need
antithrombotic therapy"

However, the ESC guidelines then go on to say:
"9.1.3 A high bleeding risk score should generally not result in withholding OAC. Rather, bleeding risk factors should be identified and treatable factors corrected"

This seems contrary to me. If HASBLED has been calculated from patients whose treatable risks haven't been treated, what's the point of it, or alternatively, if it's been calculated from patients whose risks are being managed, what's the point of the advice in 9.1.3?

15

COVID-19 / Latest Report From SAGE

« on: 12/05/2020 16:53:54 »

Sounds interesting.

16

General Science / Cheese shelf life, why?

« on: 11/05/2020 15:47:29 »

If cheese is left to mature for months, why does the packet say use within 3 days of opening? After all, cheese was invented as a means of preserving food.

17

COVID-19 / Infections: Which is the best metric?

« on: 20/04/2020 12:55:46 »

I’ve been considering whether the correct metric for comparing infection levels between countries should be absolute number, or per head of population, but I can’t make up my mind.

If the outbreak is seeded by a single infected individual, the disease will spread exponentially at a rate determined by the number each carrier infects and the time they take to do so, for as long as the uninfected population remains large enough to approximate infinity.

However, presumably most outbreaks are started by multiple travellers arriving at substantially the same time, and the number of travellers will be proportional to the population.

It's not clear why these plots are such a markedly different shape, either:
https://ourworldindata.org/grapher/daily-covid-cases-3-day-average?yScale=log&time=..&country=GBR+ESP+ITA+FRA+BEL
https://ourworldindata.org/grapher/daily-covid-cases-per-million-three-day-avg?tab=chart&yScale=log&time=..2020-03-15&country=BEL+FRA+ITA+ESP+GBR

18

COVID-19 / Coronavirus tests and death rate: cause and effect?

« on: 17/04/2020 21:40:06 »

https://ourworldindata.org/grapher/covid-19-tests-deaths-scatter-with-comparisons
This is an interesting plot, isn't it showing that countries with a lot of deaths do a lot of tests, and not that countries that do a lot of tests have fewer deaths?

19

COVID-19 / Is Lockdown Cost Effective?

« on: 11/04/2020 15:53:15 »

It would be interesting to see a list of all the major preventable causes of death, along with the costs of eliminating each. Air pollution reportedly kills 30,000 a year in the UK alone, I wonder how much that would cost to eliminate, compared with up to 24% of GDP that might be the price tag for lockdown.

20

Physiology & Medicine / Is Menthol Safe?

« on: 29/02/2020 14:46:07 »

I didn't even notice at the time, but I recently picked up a mentholated version of the shampoo I normally buy.  At first I thought I was imagining things when my face and scalp felt freezing cold in the shower, but then I noticed the vapour catching in my windpipe too. Having decided I didn't like it, I made a mental note not to pick up any more after that bottle ran out.

Anyway, by the time I'd used half the bottle I developed a bleeding sore spot in my right ear, which I just put down to a zit or something. It wasn't until I developed a matching sore in my left ear that I put 2 & 2 together. The rest of the bottle's gone down the drain now, but am I just jumping to post hoc conclusions? From the look of this website, perhaps not:

https://www.poison.org/articles/what-happens-with-swallowing-or-inhaling-too-much-menthol--174

"Menthol can cause eye and skin irritation. When used on the skin, menthol is typically diluted into a "carrier oil", lotion, or other vehicle. If a high-percentage menthol product is applied to the skin, irritation and even chemical burns have been reported. There are a few reports of people being very sensitive to menthol and having severe skin reactions to even small amounts."