Rogaine vs. Propecia - Hair Counts & Weights

But she didn't remove vellus hairs from the equation!
"Hair weight" refers to the total weight of grown hair; that
is, the total of vellus, intermediate, and terminal hairs. The vellus
hairs in a typical balding guy can obviously be a rather significant fraction
of that total weight.

Here's what _I_ think is the difference in the hair-growing
effects of Propecia and Rogaine: if a given treatment has very little
increase in total hair-counts at the same time that it significantly increases
the total weight of regrown hair (which is close to what Propecia does),
then it seems clear that its main effect is to increase the thickness
of the hair that's already there; in fact, some of the pre-existing vellus
hairs probably become intermediate hairs, some of the pre-existing intermediate
hairs become terminal hairs, and some of the existing terminal hairs become
even thicker than they were. But if another treatment produces an increase
in hair-counts which is also almost numerically identical to its increase
in total hair-weight (which is close to what Dr. Price found in her minoxidil
study), then that suggests that maybe ALL hairs are increasing in rough
proportion to that overall number. That is, brand-new vellus hairs are
being born; some of the old vellus hairs become newer intermediate hairs;
some of the old intermediate hairs become newer terminal hairs; and some
of the older terminal hairs become even thicker. And that idea is supported
by older studies which showed relative increases in ALL those classes
of hair from minoxidil treatment.

Again, Price et al counted and measured the weights of
ALL hairs. Here's a brief description of the procedure from the recent
Propecia study, which is also identical to what they did in the previous
minoxidil study:

"Evaluation procedures. Marking and hair clipping
method. At the first clipping (week -12), a plastic template with a square
hole (1.34 cm^2) was placed over the chosen scalp site. All hairs within
the designated area were pulled through the template with a crochet hook,
grasped, and carefully hand clipped intact with straight surgical scissors
under a magnifying light, which left the hair approximately 1 mm in length
at the scalp. After removal of the template, 2 small, permanent tattoos
were placed in nonadjacent corners of the square clipped area with the
use of a Spalding and Rodgers marking apparatus. [...] At each subsequent
6-week interval visit, the plastic template was placed over the target
area; the 2 small tattoos were used for accurate placement. The hair in
the target area was carefully hand clipped as previously described. The
clipped hairs were placed on prefolded, prelabeled collection paper, the
paper was folded to form a packet, and the packet was placed in a small
glassine envelope and stored until the hair samples were weighed and counted
at the end of the study.

"Hair weight determination. At the end of the initial
48-week study (week 48), hair samples collected at weeks -6, 0, 6, 12,
24, 36, and 48 were weighed in a single session by a technician who was
blinded to treatment, subject, and visit number (ie, time). [...] Before
hair was weighed, each clipped hair sample was degreased with hexane,
dried, and conditioned for at least 24 hours in a room with a constant
temperature and humidity (20 degrees C, 65% relative humidity). The hairs
were then transferred to a weighing pan and weighed in a computerized
balance with a precision of 0.01 mg. After hair was weighed, the hairs
were quantitatively returned to the packet.

"Manual hair counts. After the hair samples were
weighed, the individual hairs from the samples were laid out on a marked
grid in groups of 5 and counted manually. This procedure was carried out
at the end of the initial 48-week study for hair samples collected at
weeks 0, 24, and 48.... Hairs that were shorter than 2 mm in length were
excluded from the count, because these could represent hair shaft fragments
rather than intact hairs."

Bryan