Análisis de emisiones de la fábrica de cemento para valorizar

2005/2006 (1) (2) (3) (4)

(1) No use .676 .302 .016 .006

(2) Alcohol only .068 .810 .101 .021 (3) Marijuana+A .000 .446 .491 .063 (4) Hard drugs+A+M .092 .356 .179 .373

The interpretation of the results for the transition from 2005 to 2006 can be inter-preted similarly as the previous table. To be noticed are the different percentages on the main diagonal. The pattern here is different from the one in Table 6.13. The proportion of non-users remains the same, although a little smaller. Almost the complete majority of those who move, experiments with alcohol. The alcohol-users status becomes even more stable than before. Those who in 2005 got drunk for the first time, tend either to keep

9Please refer to Table 6.11 for the δ values, which report the proportion of subjects in each status for each year.

6.6. Conclusions

getting drunk in 2006 or to experiment with marijuana too. Across these two time points nearly all the alcohol users remain alcohol users, and only 10% start using cannabis. In opposition to the results of the previous transition matrix, the marijuana latent status becomes highly unstable. This reflects the general trend in the sample which reports a reduction in drug consumption. Now, only 50% stay, whereas the other half of the mar-ijuana users instead of moving forward to harder drugs gives up completely the use of illegal substances and goes back to alcohol use. For what concerns hard drugs users, the trend is similar to the previous transition matrix, with the only difference that those who move jump directly to the alcohol-only status instead of retreating to the closer marijuana status.

The two resulting matrices of the mover-stayer model do not differ consistently from the corresponding ones estimated in the previous section. Thus, especially for what concerns the validity of the models, it can be argued that a more complicated mixture model which isolates the non-users from the developmental process do not add much more information if compared to the computation problems involved in it. The simple models remain a valid instrument for the analysis of the sample at hand. Furthermore, the results of the mixture models confirm the validity of the previously calculated models, adding thus strength at the interpretation given to the results and to the difficulties to interpret measures of model fit.

6.6 Conclusions

Concluding, LTA analysis applies well to adolescence, a phase in the life where a lot of change is expected. Licit and illicit substance experimentation in adolescence is a re-current feature of the youths’ developmental process, and a lot of change is expected concerning their use habits. Latent transition analysis, as an instrument to test the gate-way hypothesis of substance use (Collins, 2002; Kandel & Jessor, 2002), allows to test both the existence of a specific stage sequential development among different types of substances, and the rates of transition among them. In accordance with recent studies¹⁰ that tested the gateway hypothesis using LTA, similar results have also been found.

Firstly, although the lack of information about some possible initial gateway substances, such as simple alcohol and tobacco use, the entry substance found here in the data is alcohol abuse (experiencing drunkenness). In most of the studies rewieved in Chapter 2, drinking untill drunk was always the gateway substance to the use of marijuana (Graham et al., 1991; Lanza & Collins, 2002; Maldonado-Molina & Lanza, 2010). A further con-firmation of the validity of this model is also the fact that alcohol abuse in the CriMoC sample was measured as being drunk at least once in the last year; this variable cor-responds to a broad definition of drunkenness, which varies from once a year to every week, and thus suggests that marijuana use is preceded by both light and intense abuse of alcoholic beverages. The next stage found in the sequence is marijuana use followed by other illicit substances. Also this pattern can be found in nearly any study that has tested the gateway hypothesis. This confirms once more the fact that marijuana is, at the moment and in most western cultures, the gateway drug to more dangerous substances.

Secondly, the models tested here also confirm the association among developmental stages.

Besides attesting the existence of a particular sequence, these models also show that the majority of the subjects who move across stages, move stepwise accordingly with the the-ory. In all situations, nearly all of those who move do it by moving to the next adjacent step in the sequence, without skipping any single stage. These findings also confirm the association between stages, so that being in a previous status is a necessary condition to move to a successive one (Kandel, 1975). Thirdly, the stability of the proposed

mod-10For an overwiev see Table 2.2 in Chapter 2.

els was also confirmed over time. The four developmental stages were reproduced at all four transition points (i.e., for all four models tested), suggesting that this pattern of de-velopment in the use of legal and illegal substance remains stable all across adolescence.

However, the amount of change in the transition processes was not the same at every time point. Substance use is in fact age-specific and particular substances are used mainly at particular points in life. This is the case especially for the age of onset; the four transi-tion matrices show that alcohol abuse starts early in adolescence and stabilizes at high prevalence rates with the passing of time. Somehow different is the case for illicit drugs.

Experimentation starts later and their use remains unstable across time; it seems that subjects experiment with illicit substance for a shorth period of time and then desist.

Finally, the estimated models also confirmed the assumption that backward movement is possible and expected. This is in fact the case especially for illicit substances; in late adolescence an increasing number of subjects experiment with them and then recede to the use of legal substances, which in turn tend to remain a constant habit once aquired.

A very few percentage of subjects, in fact, move back from alcohol abuse to non use.

Concluding, the time span analyzed suggests an on-going variability in use patterns for these substances; this is shown by the values on the diagonal of the transition matri-ces. Although alcohol consumption is becoming a stable and normative behavior among youths, the same cannot be stated for the other substances. Furthermore, the δ values suggest that the number of pupils getting drunk is increasing, whereas the marijuana and harder drugs users are slowly decreasing. However, the high instability of this two latter behaviors suggest an experimental consumption rather than a more systematic and prob-lematic use. In other words, the proportion of alcohol users is constantly increasing and this behavior is systematically becoming part of the youths’ behavioral repertory. Illicit drug use, on the other hand, after having reached a peak between the age of 15 and 16, starts to decrease and rather than as a systematic and problematic consumption, it seems to resemble a more generalized occasional and experimental use.

Chapter 7