It is well known how difficult it is for users of illegal drugs to have access to reliable information regarding the composition and purity of the substances they consume. This disempowerment in the face of risks posed by adulterations and variations in dose results in the emergence of reasonable doubts concerning drug quality, and favors the proliferation of unfounded myths. Debates on the topic of illegal drug use are—at best—circular and sterile, while legal drug use largely avoids being debated in the first place. There is no doubt whatsoever that a lack of reliable information is the norm for each and every illegal drug. Yet it is also true that governmental health services and other institutions sometimes surprise us, often through the media, by presenting partial data regarding the purity and composition of substances such as heroin and cocaine. Interesting research has also been presented recently on cannabis, as well as on MDMA. However, LSD is a case unto itself; in general terms, the decades-long lack of access to this kind of information for LSD is shocking.

Attempting to overcome this situation, to the best of our capacity, we have compiled the results of a series of laboratory tests carried out with LSD samples from the 1970s to 2005. We do not intend to be definitive or exhaustive in our presentation of the issues related to the composition of the samples. Yet, we believe that the data we offer will help shape an approximate idea about what compounds and quantities are contained in illegal-market acids, and the degree to which their purity and composition have changed over the years.

We will start by commenting on recent research conducted in September 2005 and published a month later by Interviú magazine in an article written by Alberto Gayo. The analysis was carried out by the Spanish Medicines and Health Care Products Regulatory Agency, a department of the National Health Service. The analysis techniques that were used were high performance thin-layer chromatography (HPTLC), high performance liquid chromatography (HPLC) using a high-quality silica column, and gas chromatography–mass spectrometry (GC–MS). The putative LSD samples were provided to Interviú by Energy Control.

Eleven samples from different sources in Spain were analyzed. LSD was detected as the only substance present in all the samples; 19 micrograms was the minimum quantity detected, 102 µg was the maximum quantity detected, and 38.81 µg was the average quantity detected. (see Table I)

Table I. Analysis of Spanish LSD Samples - September 2005 Spanish Medicines and Health Care Products Regulatory Agency
Sample Number	Image*	Type of Sample	Place of Origin	Drugs Detected	Quantity of Active Principle (in micrograms)
1		Black microdot	Barcelona	LSD	20 µg
2		Star	Barcelona	LSD	26 µg
3		Marilyn	Madrid	LSD	19 µg
4		Galaxy	Madrid	LSD	26 µg
5		Black microdot in star shape	Barcelona	LSD	23 µg
6		Yellow microdot	Barcelona	LSD	26 µg
7		Little Bear	Barcelona	LSD	94 µg
8		Red, black and white blotter	Barcelona	LSD	102 µg
9		Internet Explorer	Bilbao	LSD	37 µg
10		Doll	Barcelona	LSD	35 µg
11		Pink triangle	Barcelona	LSD	19 µg

Six additional samples from Switzerland that had been sent to Energy Control by Eve & Rave were analyzed. The active compound detected in every one of them was LSD; 25 µg was the minimum quantity detected, 79 µg was the maximum quantity detected, and 50.1 µg was the average quantity detected. (see Table II)

Table II. Analysis of Swiss LSD Samples - September 2005 Spanish Medicines Regulatory Agency under the National Health Service
Sample Number	Image*	Type of Sample	Place of Origin	Drugs Detected	Quantity of Active Principle (in micrograms)
1		Alien	Switzerland	LSD	79 µg
2		White Blotter	Switzerland	LSD	41 µg
3		Shiva	Switzerland	LSD	28 µg
4		Cloud	Switzerland	LSD	59 µg
5		Little Bear	Switzerland	LSD	25 µg
6		Green Pistachio Blotter	Switzerland	LSD	69 µg

In light of these data, it can be concluded that these Spanish and Swiss samples from 2005 contained what they were supposed to contain: lysergic acid diethylamide, with no added compounds. The average quantities (38.81 µg and 50.1, µg respectively) are low doses with very slight visuals-inducing capacity. Paradoxically, lower doses such as these can sometimes produce anxiety (particularly within a setting of sensory over-stimulation, as is associated with the night life scene) since placing a user only half-way into a psychedelic experience may increase his or her resistance to letting go and flowing with the experience, which can be easier to do with higher doses. A surprising number of the samples contain close to threshold doses: that is, amounts that produce slight stimulation and a mild alteration of perception. Quantities with substantial psychedelic potential were detected in only two cases (94 and 102 µg). However, such a small number of samples might not be representative, and to have a better picture of the material available on the black market, it would be necessary to compare these results with data obtained by other institutions and agencies.

The Drugs Department at the National Institute of Toxicology (INT) is the Spanish laboratory of reference for the United Nations within the International Collaborative Exercise (ICE), organized by the United Nations Development System (UNDS). Among other tasks, INT's Drugs Department is in charge of the analysis of all substances confiscated by the police in Madrid and other parts of the Spanish national territory in their pursuit of drug trafficking, possession, and public consumption of illegal drugs. Whenever legal proceedings begin for trafficking or possession of illegal drugs, an analysis is carried out to make sure that the material confiscated contains an illegal substance. After the INT analyzes either small amounts confiscated from personal users or large amounts seized from dealers, its Memorias act as an excellent report on the composition and purity of different drugs from the Spanish black market over the last few years. However, the number of LSD-related analysis results is small in comparison to results for cannabis, heroin, cocaine and MDMA. While such reports are clearly of value, their scope is limited.

From 1997 until 2003 (the last year for which data had been reported at the time this article was written), the INT—using the same laboratory techniques that the National Medicines and Health Care Products Regulatory Agency used in the 2005 report mentioned above—analyzed 2,189 samples (Table III): 2,182 were blotter, one was powder, and six were liquid.

Of the 2,182 blotters analyzed, all but one contained LSD, and no adulterants were found in any of them. The blotter that did not contain LSD, printed with a black and blue yin/yang symbol, contained a mixture of amphetamine, methamphetamine and temazepam (a benzodiazepine); specific amounts of each drug were not reported. The minimum quantity detected in the other 2,181 samples was 25 µg, maximum quantity was 148 µg, and average quantity was 29.94 µg. However, there was a single seizure of 1,938 hits of blotter, each with a quantity of 25 µg, that might be distorting the results; if we disregard that seizure, the average quantity of LSD is 69.22 µg.

The average quantity (29.94 µg) of samples analyzed by the INT from 1997 to 2003 is lower than the average quantities analyzed by the Spanish Medicines and Health Care Products Regulatory Agency in 2005 (38.81 µg for Spanish samples and 50.1 µg for Swiss), or slightly higher if we disregard the large single seizure of uniformly dosed 69.22 µg hits from 1997. Breaking down average quantities (Table IV) shows that in several years, the quantities reported were merely threshold or low doses (26.48 µg or 54.56 µg; 57.44 µg and 55.93 µg), similar to those found in the 2005 analysis. It is also clear that some variability exists, since we can see average concentrations of 83.74 µg (1999) and 118 µg (1998).

At this point one may wonder whether these results apply only to the Spanish market in the late 1990s and early 2000s, or if—on the contrary—they also apply to other countries and decades.

Table III. LSD Sample Analysis by the Spanish Toxicology Society, 1997-2003 Source: Memorias, National Institute of Toxicology (INT)
Type of Sample	# of Samples in Seizure	Drugs Detected	Dose (in micrograms)	Image Printed on Sample
Year 1997 2041 samples				Donald Duck, blue star on white background, green and yellow background with mark 19, two purple and brown intertwined silhouettes, Indian-shape figures with blue star on white background
Blotters	1	LSD	145.6 µg/dose
Blotters	2	LSD	26 µg/dose
Blotters	6	LSD	125 µg/dose
Blotters	15	LSD	73 µg/dose
Blotters	29	LSD	38 µg/dose
Blotters	50	LSD	49.3 µg/dose
Blotters	1938	LSD	25 µg/dose
Year 1998 31 samples				Cloud on yellow background, penguin on white background, horse, cat with the carving "Eddy's cat", colored imprints, irregular drawings of various colors, pink colors on white background
Blotters	6	LSD	115 µg/dose
Blotters	20	LSD	131 µg/dose
Blotters	1	LSD	25 µg/dose
Blotters	1	LSD	69.5 µg/dose
Blotters	1	LSD	88.5 µg/dose
Blotters	1	LSD	148 µg/dose
Blotters	1	LSD	54.5 µg/dose
Year 1999 51 samples				Colored imprints, cyclist drawing and colors drawings
Blotters	48	LSD	83 µg/dose
Blotters	1	LSD	77.5 µg/dose
Blotters	1	LSD	69.5 µg/dose
Blotters	1	LSD	140 µg/dose
Year 2000
	No LSD analysis
Year 2001 27 samples
Blotters	8	LSD	68 µg/dose	Bart Simpson
Blotters	15	LSD	45 µg/dose	Ferrari logo
Blotters	4	LSD	83 µg/dose	Green palm of hand
Year 2002 38 samples
Blotters	19	LSD	55 µg/dose	Green background with sunflowers
Blotters	2	LSD	70 µg/dose	Face
Blotters	11	LSD	55 µg/dose	Head
Dust Sample	1	LSD	88.5% LSD
Liquid Sample	1	LSD	87.5 µg/ml
Liquid Sample	1	LSD	90 µg/ml
Liquid Sample	1	LSD	42.5 µg/ml
Liquid Sample	1	LSD	133 µg/ml
Liquid Sample	1	LSD	904 µg/ml
Year 2003		LSD
	1	Amphetamine, methamphetamine and temazepam	Not indicated	Black and Blue Yin Yang
Total	2189	samples analyzed

For years, the Drug Enforcement Agency (DEA), whose task is to enforce drug laws in the United States, has tested the composition and purity of all kinds of forbidden psychoactive substances, LSD among them. At Erowid.org, one can access an archive with results obtained in the decade 1976–1986. Within this file, named The LSD Blotter Index, are the test results of 134 varieties of blotters allegedly sold as LSD. In all the samples except for one, the sole substance detected was lysergic acid diethylamide. The one exception contained 21 µg of DOB and no LSD. The minimum quantity of acid found in a sample was 5 µg, the maximum was 220 µg and the average was 52.25 µg. According to the DEA, the blotters' quantities are generally between 20 and 80 µg, with 50 µg being what they consider a "standard dose". The Erowid website expressed some doubts regarding the reliability of this data, due to possible clashes of interests or due to the lack of information regarding the techniques used to perform the analyses. However, such doubts do not automatically cancel out the validity of this information, and the results reported largely coincide with those obtained by distant, distinct institutions such as the INT and the Spanish Medicines Agency.

PharmChem Laboratories in California was another source for LSD analysis. In the 1970s, PharmChem carried out tests on samples sent to its facility by drug consumers themselves; a list of results obtained from 1972 to 1974 can be accessed at Erowid. In this list, 514 samples were submitted as LSD. They came in different forms: on paper or sugar cubes, in tablets, capsules, gel, or liquid, and soaked onto mushrooms. Forty-three of these samples (8.3%) did not test positive for LSD, or they had LSD plus another substance (PCP, amphetamine, methamphetamine, pseudoephedrine, DOM, or ergot derivatives). The other 91.7% contained LSD with no adulterating substances: 44 samples (8.5%) contained LSD plus iso-LSD (an allegedly non-psychoactive isomer); 5 samples (0.9%) contained LSD marked as impure; for the remaining 422 samples (82.1%) LSD was the sole substance detected. LSD quantities were expressed in micrograms for 156 samples, with 5 µg being the minimum quantity found (although some others merely had a "trace" amount), 475 µg was the maximum quantity in a single sample, and 78.8 µg was the average quantity.

In 1977, PharmChem published a review of the analyses it carried out on samples sold as acid from 1969 to 1975. Out of the 2,200 samples tested, 87% contained LSD with no other compound. The minimum quantity detected was 5 µg, the maximum quantity was 500 µg, and the average quantity was 75 µg.

Data concerning the composition and purity of liquid and powdered LSD can largely be considered anecdotal. In 2002, the Spanish Toxicology Society tested 5 samples; all of them had LSD as their only psychoactive compound: 42.5 µg per ml, 87.5 µg per ml, 90 µg per ml, 133 µg per ml, and 904.5 µg per ml. These amounts represent amazingly low concentrations, especially taking into account that the standard dose for liquid LSD is a single drop (and there are approximately 20 drops in a ml). This is why a drop of any of the samples analyzed by the INT could only be described as anything between "low" and "plainly ridiculous". In the PharmChem tests there were four samples of liquid LSD that contained only LSD as the active principle. The detected quantities were 55 µg per drop in three cases and 75 µg per drop in the fourth case. There was also a fifth sample that contained "ergot derivatives". Finally, one of the samples tested in 2005 by the Spanish Medicines Agency was liquid LSD on blotter paper. The detected substance was indeed LSD, but the dose was merely 19 µg.

Regarding samples of LSD powder, the INT analyzed one in 2002 that was 88.5% pure. The DEA describes an average concentration as being around 62% (with the remaining percentage being non-psychoactive isomers, rather than adulterating compounds), although some has been reported as being 95–100% pure. We should also take into account the fact that, according to PharmChem's tests, some of the samples that contained neither LSD nor any other psychoactive substances were in powder form.

The data we have reviewed so far indicates that the vast majority of substances sold as LSD are, in fact, LSD, with no other psychoactive chemicals or adulterating substances. Out of the 134 blotters analyzed by the DEA between 1976 and 1986, only one contained DOB instead of acid. Similarly, out of the 2,189 samples analyzed by the INT between 1997 and 2003, only one did not contain LSD; instead, it contained amphetamine, methampethamine, and temazepam. Out of 2,323 samples, therefore, there was a 0.08% percentage of adulteration or misrepresentation. PharmChem's results showed an 8.3% adulteration or misrepresentation in the 514 samples analyzed in the period 1972–1974 and a 13% adulteration or misrepresentation in the 2,200 samples analyzed in the years 1969 to 1975. It is relevant to point out that in those years, some analyzed samples were presented in tablets or capsules, which are more easily adulterated with other substances than blotters are. Out of the 514 samples tested by PharmChem in 1972–1974 there were only four cases of fraudulent blotter hits: two contained no drug at all, one contained DOM, and the remaining one contained LSD and PCP. The rest of adulterations occurred in forms of LSD that have not been seen for years. It may be concluded that, since the 1970s, adulteration of blotter and microdots is rare, and that the INT's finding of blotter containing amphetamine and benzodiazepine derivatives is highly unusual. We contacted the INT to learn whether this result might be a mistake, and we were told that it was not. This oddity—the exception that proves the rule—also confirms that no other psychoactive substance was detected in the rest of the samples because there was none to be detected. If there had been any other substance, it would have been detected just like the temazepam and amphetamines were detected, or just like the DEA had detected DOB. Regarding the latter substance; DOB on blotter does not necessarily imply a fraud, since DOB on blotter is often deliberately produced and bought and sold as DOB, not as LSD. It is also worth mentioning that the amounts of temazepam and amphetamine that a blotter hit could hold would produce barely noticeable psychoactive effects if orally consumed. It is theoretically possible – though no data exist to support or refute this idea – that even small amounts of such substances, interacting with LSD in the same sample, may cause some synergistic or altered psychoactive effects. Reported analysis statistics, however, render this hypothesis irrelevant in the real world; at an adulteration rate of 0.08%, if a single person consumed 10,000 dose units of LSD, he might experience the aforementioned speculative effects on only eight occasions.

A totally different issue is that of the real amounts of lysergic acid contained in black market samples. Looking at the average concentrations obtained in any given period or year, one will see that the most frequent value is fifty µg. The absolute average concentration of all the tests already mentioned (excluding the INT results for powdered and liquid samples) is exactly 53.38 micrograms (Table IV).

Table IV. Minimum, average and maximum concentrations of the different analyses carried out by several institutions from the 1970s to the present day. Absolute average concentration, counting all the analyzed batches: 53.38 µg. INT's powder and liquid samples that are discussed above are excluded.
Year	Quantity of Analyzed Samples	Minimum Concentration	Average Concentration	Maximum Concentration
2005 Medicines Agency, Spanish Samples	11	19 µg	38.81 µg	102 µg
2005 Medicines Agency, Swiss Samples	6	25 µg	50.1 µg	79 µg
2002 INT	32	55 µg	55.93 µg	70 µg
2001 INT	27	45 µg	57.44 µg	83 µg
1999 INT	51	69.5 µg	83.74 µg	140 µg
1998 INT	31	25 µg	118 µg	131 µg
1997 INT	2.041	25 µg	26.48 µg 54.56 µg (excluding a batch of 1938 samples)	145.6 µg
1976-1986 DEA	134	5 µg	52.25 µg	220 µg
1972-1974 PharmChem	156	5 µg	78.8 µg	475 µg
1969-1975 PharmChem	2200	5 µg	75 µg	500 µg

It might be concluded that the dose most frequently contained in black-market LSD samples is generally low, which would make them suitable for recreational use by those searching for easily managed effects. Yet, should we take into account that most users in Spain consume just a portion of the whole blotter hit (a quarter, a third or a half), it is obvious that many contemporary samples of LSD will cause little more than the threshold effects of slight stimulation and soft distortion of perception. In many cases, people wishing to experience full psychedelic effects would have to ingest 2–6 or more blotter hits. Exaggerated as this may seem, a simple calculation will show that it is not. It is enough to go over the LSD samples analyzed by the Spanish Medicines Agency in 2005 and calculate how many dose units of each of them it would be necessary to consume in order to reach a 250 µg dose (Table V).

Table V. Number of dose units of samples analyzed in 2005 that are necessary to reach a 250 µg dosage
Sample	Amount of LSD Detected	Number of Dose Units Necessary to Reach 250 µg
Black microdot	20 µg	12.5
Star	26 µg	9.6
Marilyn	19 µg	13.15
Galaxy	26 µg	9.6
Star microdot	23 µg	10.8
Yellow microdot	26 µg	9.6
Little bear	94 µg	2.6
Red, black and white	102 µg	2.4
Internet Explorer	37 µg	6.7
Doll	35 µg	7.14
Pink triangle	19 µg	13.15
Alien	79 µg	3.16
White	41 µg	6.09
Shiva	28 µg	8.9
Cloud	59 µg	4.23
Little bear	25 µg	10
Green	69 µg	3.62

According to the results in Table V, the minimum amount necessary to reach the aforementioned dose would be 2.4 dose units, the maximum would be 13.15 dose units, and the average would be 7.8 dose units. If we perform the same calculation using the average quantities of LSD detected in previous decades, we find that, according to INT's analysis from the period 1997–2003, taking as valid the average value of 29.94 µg, it would have been necessary to consume 8.3 dose units to reach 250 µg. (In general terms, it would have been enough in most of those years to consume five, and sometimes even less.) For the period 1976–1986, according to DEA's results, five dose units would have been necessary to reach that value. In the period 1972–1974, 3.17 dose units would have been necessary, or 3.3 dose units if we take into consideration the full period covered by PharmChem's tests (1969–1975). In the mid-1960s, the situation was quite different, since at that time the most important black market LSD manufacturer (Owsley Stanley) distributed acid at a standard concentration of 270 µg.1 And of course there was pharmaceutical LSD from Sandoz (Delysid), available up until 1966, for which the user knew the concentration and could calculate precisely measured doses.

It is quite clear that there has been a reduction in the lysergic acid diethylamide content in black-market acid; in order to achieve a strong psychedelic experience of about 250 µg in the mid-1960s, one dose unit was enough; in the 1970s, about three would be required; in the 1980s, the number rose to five; and in the 1990s (as well as in the twenty-first century), it rose to five to eight.

We might wonder, at this point, about the possible causes for what could be described as the slow decline of the psychedelic potential in street acid. A feasible hypothesis could be that the ongoing expansion of the recreational uses of drugs has come to demand ever lower LSD doses, in order to make it more suited to the sought-after effects in the context of night-time leisure for youth, where LSD is often consumed. It might be concluded that the public at large is more interested in the recreational effects provided by low doses than in the profoundly altering psychedelic experiences of higher doses, which have come to be appreciated only in some environments by connoisseurs. Perhaps the market just adjusted to its customer's demands. The gradual narrowing of the range of quantity of LSD per dose unit throughout the years can be argued in support of this hypothesis (putting aside the reduction of average quantities), so that those amounts are ever closer to what we would describe as a low dose. In this manner, Owsley's 270 µg acid from the mid-1960s gave way in the 1970s to quantities between 5 and 500 µg, whereas in the 1980s (according to the DEA), those margins narrowed between 5 and 220 µg, and in the two following decades, they went from 20 to 100+ µg (145.6 µg in 1997 and 102 µg in 2005).

The recurring argument that street acid today is more stimulating and less mystical or psychological in effect may be explained by the gradual reduction in the dose, instead of a reduction in quality. In fact, the amounts of LSD per dose unit found in the last few years are precisely those that only produce light stimulation and soft distortion of perception, and are clearly not sufficient to induce a significant psychedelic experience. With regard to quality, the results obtained so far show that almost everything that is sold and bought as LSD really contains LSD, with no psychoactive compounds as adulterants.

If there is no adulteration occurring, this implies that variations in effects from different samples, rather than being due to variations in quality and purity (as is often argued), are caused by the differences in the dose consumed (from 20 to 100 µg), and by the consumer's set and setting, which are different on each occasion LSD is consumed. As well, the effect of numerous other psychoactive substances of unknown composition and dose, which are often deliberately mixed with LSD by consumers (at least in the context of recreational use), make it even harder to attribute any variation in the experience solely to the LSD consumed.

The differences some people sensed when contrasting the effects of street acid with Sandoz pharmaceutical LSD could be explained through variations in the dose. They could also be explained through opposite expectations: consumption of a product from the pharmaceutical industry is viewed as "safe", because purity and dose are assured, whereas the consumption of a black-market product causes the consumer to be suspicious of its quality, its content, and its quantity. In the event that such a comparison was performed with samples of illegal acid of a known high dose, such as Owsley's 270 µg acid, there is no doubt that the reduction in the dose of today's acid would be sufficient to explain the variations in effect. On a personal level, we take this as the most feasible explanation, especially given that, for the time being, explanations based on the differences in composition have been refuted time and time again. When someone disputed that street acid really contained LSD, its presence was confirmed by laboratory tests. When the reliability of the analysis techniques was questioned, LSD's presence was again proven with new reliable techniques. When it was argued that the samples had to be adulterated with other psychoactive substances, it was proven that adulterating compounds are so uncommon that their use is merely anecdotal: the exception that proves the rule. Currently, the debate focuses on any possible psychoactive influence that synthesis impurities might cause, which would be present in street acids and not, one presumes, in Sandoz Delysid. In light of similar debates regarding other substances, such as ketamine and MDMA, one tends to disregard such potential influence as unlikely. However, it is true that, as of today, no one has provided a definitive answer on the matter. The debate remains open and is not likely to be resolved in the short term, since access to pharmaceutical LSD and sophisticated laboratory techniques of analysis are both limited.

This said, we would like to end this chapter with some final comments. First, in relation to consumption, it would be appropriate to keep an eye on the characteristic variability of the black market. Among the samples tested in 2005, some are five times more potent than others (from 19 µg to 102 µg); so in order to consume a 250 µg psychedelic amount, it would be necessary to take 13 dose units of some blotters and just 2.5 dose units of other blotters. That calls for a cautious approach toward consumption, beginning with low amounts and increasing them until reaching the desired effects on following occasions, in spite of the annoying time-consuming aspect of such a method.

One could argue that—based on the results obtained in laboratory analyses—to enjoy recreational experiences in party environments, it can be sufficient to consume less than a single dose unit of LSD (a quarter, a half, or a third of a hit). However, for psychonautic uses, one could say that—considering these same lab results—cutting blotter hits in half or into quarters seems truly senseless. (Should someone think we are exaggerating, we encourage him to divide by two and by four the aforementioned minimum, average, and maximum amounts.) It is also obvious that while this kind of advice might suit the present day situation, it could be inappropriate in the future due to the black market's instability. No one knows what the LSD content of blotter will be in two, five, or ten years' time. It is the user's responsibility to adjust his consumption guidelines to the estimated content of each sample. For this reason, it is always wise to show caution when consuming the first dose of each batch.

It is also worth mentioning that LSD rapidly degrades in the presence of light, heat, and oxygen. Employing careful storage practices will go a long way toward preserving potency: tightly wrap in aluminum foil, place the foil into a ziplock baggie, and then put the baggie along with some silica gel inside a sealed glass jar and store it in a freezer.

Finally, there are commercially available LSD-testing kits. If these kits show a negative result, you can be certain that your sample does not contain LSD. If they show a positive result, this may indicate that your sample does contain LSD (although there are other compounds that can give false positive results). Nevertheless, considering how easy it is to purchase acid-free "vanity" blotter art these days for low prices from Internet-based companies, such test kits could be helpful in weeding out any "blank" acid that unscrupulous dealers might be selling.

We gratefully acknowledge O.G.'s and Dominic Pfäffli's work in collecting the samples, Alberto Gayo for allowing us to reproduce his article's data, and José Carlos Bouso for his suggestions.