Thread: Identifying a convex bevel caused by extensive pasted stropping

Originally Posted by Jimbo

I suppose it's a bit like that Ed, but not entirely.

Basically, without getting too technical, what is going on is what's known as an ordinal scale. It is not the same as a numerical or ratio scale, where we can say that 4 is twice as big as 2 and so on, but it is not quite as arbitrary as a completely categorical system (where we can interchange the labels so long as we remember what they mean - eg we might label patients in a drug trial as A = drug group and B = control group, but the labels can be swapped - or are arbitrary- so long as we keep track of which label refers to which group).

So the HHT-x is ordinal - the x's are categories, but there is order associated with them ie 1 < 2 ... < 5. Now there's nothing wrong with that at all from an internal consistency perspective, obviously. I know what I mean by the numbers, and in fact as I gain more experience using the scale I will most likely jigger and readjust things until I get the scale just how I like it and it will be quite useful for me.

Problems arise, however, with inter-person use. There are two main issues: location and scale. I think I can demonstrate both of these diagrammatically, but don't hold me to that

The location issue is where two people start the scale. My HHT 1, because of my hair type, may in fact correspond to your HHT 2 for example. That is, on the same edge my hair would, say, simply split whereas your hair may in fact cut through. So we'd be out of sync like this, for example:

1 *** 2 *** 3 *** 4 *** 5
.........1 *** 2 *** 3 *** 4 *** 5

The other problem is scale. Ordinal scale cut offs cannot be assumed to be equi-distant (as I pictured above). Different individuals may have different "elasticities" between cut offs:

1 ***** 2 ** 3 * 4 ****** 5
1 ** 2 **** 3 ** 4 **** 5

And of course there could be combinations of scale and location differences between people too.

There's a rather large literature in the mathematical and, more particularly statistical, literature on this kind of thing. As a general rule, any proposed measure of something using this kind of scale needs to be assessed both for its intra-person reliability (which for HHT-x I think is probably quite good after a bit of calibration) and its inter-person reliability (which is where I think the HHT-x really falls down).

Of course, poor inter-rater reliability of the HHT-x is pure (educated) conjecture on my part. I could quite possibly be very wrong. The only way to find out would be to conduct inter-rater testing which would involve many raters assessing the HHT-x behaviour of an identical set of edges independently of each other. If anyone wants to do that I'd be more than happy to advise the experimental design, and I'll even throw in the analysis and waive my usual consultation fee

Please also note that unless coticules somehow impart hair homogeneity to everyone who hones with them, the problems I've outlined above are not non-coticule specific I'm afraid.

James.

And as the "trial" went on the identical blades would become non identical, as everyone would have to use the same part of the edge to ensure consistency to ad great a degree as possible, but I suppose the blade could be sent back to a control after every x number of tests and the degree of drop off could be measured and recorded.

Originally Posted by edhewitt

And as the "trial" went on the identical blades would become non identical, as everyone would have to use the same part of the edge to ensure consistency to ad great a degree as possible, but I suppose the blade could be sent back to a control after every x number of tests and the degree of drop off could be measured and recorded.

You forgot the part about everyone using/having the same type of hair

The only way to get consistency with this test would be to use synthetic hair extensions and I'm not sure that is even consistent batch to batch or brand to brand.

Originally Posted by Catrentshaving

You forgot the part about everyone using/having the same type of hair

I also forgot about the contract we would need to engage mythbusters for. We will need a machine that holds the hair at a certain point, clamps the blade at a fixed angle in relation to the hair, and swung it with identical speed and force.
Oh I think the hair issue was covered in a different thread, I suggested that we engage someone as a standard head to be used for various tasks such as brush scratchiness, ability of a soap to lather, comparative blade harshness versus sharpness etc, and they would also provide standard hairs.

Originally Posted by Jimbo

I suppose it's a bit like that Ed, but not entirely.

Basically, without getting too technical, what is going on is what's known as an ordinal scale. It is not the same as a numerical or ratio scale, where we can say that 4 is twice as big as 2 and so on, but it is not quite as arbitrary as a completely categorical system (where we can interchange the labels so long as we remember what they mean - eg we might label patients in a drug trial as A = drug group and B = control group, but the labels can be swapped - or are arbitrary- so long as we keep track of which label refers to which group).

So the HHT-x is ordinal - the x's are categories, but there is order associated with them ie 1 < 2 ... < 5. Now there's nothing wrong with that at all from an internal consistency perspective, obviously. I know what I mean by the numbers, and in fact as I gain more experience using the scale I will most likely jigger and readjust things until I get the scale just how I like it and it will be quite useful for me.

Problems arise, however, with inter-person use. There are two main issues: location and scale. I think I can demonstrate both of these diagrammatically, but don't hold me to that

The location issue is where two people start the scale. My HHT 1, because of my hair type, may in fact correspond to your HHT 2 for example. That is, on the same edge my hair would, say, simply split whereas your hair may in fact cut through. So we'd be out of sync like this, for example:

1 *** 2 *** 3 *** 4 *** 5
.........1 *** 2 *** 3 *** 4 *** 5

The other problem is scale. Ordinal scale cut offs cannot be assumed to be equi-distant (as I pictured above). Different individuals may have different "elasticities" between cut offs:

1 ***** 2 ** 3 * 4 ****** 5
1 ** 2 **** 3 ** 4 **** 5

And of course there could be combinations of scale and location differences between people too.

There's a rather large literature in the mathematical and, more particularly statistical, literature on this kind of thing. As a general rule, any proposed measure of something using this kind of scale needs to be assessed both for its intra-person reliability (which for HHT-x I think is probably quite good after a bit of calibration) and its inter-person reliability (which is where I think the HHT-x really falls down).

Of course, poor inter-rater reliability of the HHT-x is pure (educated) conjecture on my part. I could quite possibly be very wrong. The only way to find out would be to conduct inter-rater testing which would involve many raters assessing the HHT-x behaviour of an identical set of edges independently of each other. If anyone wants to do that I'd be more than happy to advise the experimental design, and I'll even throw in the analysis and waive my usual consultation fee

Please also note that unless coticules somehow impart hair homogeneity to everyone who hones with them, the problems I've outlined above are not non-coticule specific I'm afraid.

James.

"As a general rule, any proposed measure of something using this kind of scale needs to be assessed both for its intra-person reliability (which for HHT-x I think is probably quite good after a bit of calibration) and its inter-person reliability (which is where I think the HHT-x really falls down)." -TOTALLY AGREE. It is as simple as a nurse asking someone to rate their pain on a scale of 1-10 AKA a Likert scale which is a psychometric scale commonly used in research. Yes, HHT is subjective as is most of your tests for sharpness. If you read my responses I believe that is what you will find me saying. Even a shave test will have problems between people. Lets face it (yup pun intended) what works for you may work for me OR it may not! That is my point here people. Lets not get all caught up in thinking that YOUR way is the best or only way or YOUR test is ANY better than someone elses. A shave test has it's faults and shortcomings too. When you say you test shaved with my razor and it was fine for you what does that mean to me? Nothing! It may or may not shave fine for me. I don't know until I try it.

Now if you are talking testing your OWN blade with YOUR face then that is just as valid as testing your OWN blade with your CALIBRATED hair.

I see so many heated discussions on this board (by mainly the same people) about HHT that I am beginning to wonder if some people are just upset that they cannot get their razors sharp enough to pass the HHT and just wish everyone would stop using it? (Oh no he di'nt! Oh yes he did!) Of course, YMMV.

Originally Posted by Ryan82

2. When you use pastes you're out of the realm of stropping and into the realm of honing. I respect Glen's experiments and opinion and I'm not calling the shaving comfort factor into question. But when this question comes up I do question the amount of metal being removed by using pastes every shave. If you use the same razor every day and strop on pastes 40 times every shave I guarantee you'll see some metal removed over 365 days. It might seem negligible but give it years or decades and the lifespan of that razor will be reduced.

Actually, I guess some people who have a lot of experience here believe that the .1 Micron paste does not remove enough steel to shorten the lifespan of a razor as it is so small it is negligible. My opinion is that everyone here is just giving an educated guess but I will let you know in about 40 years if my Dovo has been affected at all.

Hmmmmmmm.............

OK, Your way is the best!!

Happy Now.........

Ps, I am not against HHT's except when new guys who read all about them take an oiled razor and try the HHT as their measure of sharpness and proclaim a razor dull.

In any case, every time I try an HHT, I still end up seeing how the razor shaves. Sometimes, in my experience, the HHT works and the shave is not good. Sometimes, the HHT fails and the shave is great.

Have fun

Originally Posted by Steel

"As a general rule, any proposed measure of something using this kind of scale needs to be assessed both for its intra-person reliability (which for HHT-x I think is probably quite good after a bit of calibration) and its inter-person reliability (which is where I think the HHT-x really falls down)." -TOTALLY AGREE. It is as simple as a nurse asking someone to rate their pain on a scale of 1-10 AKA a Likert scale which is a psychometric scale commonly used in research. Yes, HHT is subjective as is most of your tests for sharpness. If you read my responses I believe that is what you will find me saying. Even a shave test will have problems between people. Lets face it (yup pun intended) what works for you may work for me OR it may not! That is my point here people. Lets not get all caught up in thinking that YOUR way is the best or only way or YOUR test is ANY better than someone elses. A shave test has it's faults and shortcomings too. When you say you test shaved with my razor and it was fine for you what does that mean to me? Nothing! It may or may not shave fine for me. I don't know until I try it.

Now if you are talking testing your OWN blade with YOUR face then that is just as valid as testing your OWN blade with your CALIBRATED hair.

I see so many heated discussions on this board (by mainly the same people) about HHT that I am beginning to wonder if some people are just upset that they cannot get their razors sharp enough to pass the HHT and just wish everyone would stop using it? (Oh no he di'nt! Oh yes he did!) Of course, YMMV.

Originally Posted by Lynn

Hmmmmmmm.............

OK, Your way is the best!!

Happy Now.........

Ps, I am not against HHT's except when new guys who read all about them take an oiled razor and try the HHT as their measure of sharpness and proclaim a razor dull.

In any case, every time I try an HHT, I still end up seeing how the razor shaves. Sometimes, in my experience, the HHT works and the shave is not good. Sometimes, the HHT fails and the shave is great.

Have fun

Exactly, that is not a very good use for the HHT. I use it only during honing, along with other tests, to gauge my progress and see if the blade is getting sharper and whether one section is remaining dull etc. It's the only valid use as far as I can see. I certainly would not want to shave my face halfway through honing just to see how it feels

Originally Posted by Kefka

Exactly, that is not a very good use for the HHT. I use it only during honing, along with other tests, to gauge my progress and see if the blade is getting sharper and whether one section is remaining dull etc. It's the only valid use as far as I can see. I certainly would not want to shave my face halfway through honing just to see how it feels

As I stated before, the hair on my head won't be cut by even the sharpest blade...and not because my honing isn't up to snuff either...it's just that fine. So I rely on the Thumb Pad Test and if the blade will cut hair above the skin on my arm or leg. These are the tests that over time are proven with my honing.

Yeah of course that is always an issue with finer hair and that's fine, there's other ways to check your progress as you've mentioned and I use those too. I just happened to have an easy source of hair which is not too thick or thin (chest hair ) so I find it very handy to grab one and test.