Density probability plots

Probability plots are popular and effective tools for the graphical assessment of the goodness-of-fit of a given dataset to a hypothesised probability distribution, F say, with density f. The user can easily see any departures from F that there are, but the interpretation of such departures may not be immediately apparent. (It may take some time to work out their meaning, or else to resort to a set of rules for the interpretation of probability plots.) We investigate whether instant interpretability of these tools can be aided by a simple transformation which transfers visual assessment to the realms of familiar and immediate comparisons between densities. We seek to do so without smoothing, and see how far this allows us to go. The idea is very effective, and rather more so than quantile-quantile plots, for f's that have a single peak when the density g from which the data truly come is also unimodal. The idea is much less appealing, however, when f and g have different modalities from each other

Eliminação de anomalias fisiológicas, in vitro, de plântulas de pessegueiro Recovering of anomalous peach seedlings growing in embryo culture

O experimento objetivou eliminar os sintomas de roseta e ananismo em híbridos de pessegueiro (Prunus persica L. Batsch) precoces, provenientes de cultura embrionária. Essas anomalias fisiológicas aparecem em vista dos inibidores de crescimento presentes nos meristemas apicais dos embriões. Dois processos de recuperação de vitroplântulas anômalas foram adotados: (a) eliminação da porção apical logo acima da primeira gema, a partir dos cotilédones; (b) manutenção das vitroplântulas por trinta dias em ambiente de vernalização com temperatura de 5-10 º C. Os melhores resultados foram obtidos quando se eliminou a dominância do meristema apical; as vitroplântulas mantidas em sala de crescimento emitiram, em cinco dias, brotações novas e normais e se desenvolveram rapidamente. Aquelas submetidas à quebra de endodormência, porém,retomaram parcialmente o desenvolvimento, de forma lenta e anormal.<br>Two methods were studied on peach embryo culture in order to recover seedlings presenting rosette and dwarf development. In the first method almost all the epicotyle was eliminated. Only a small portion of the axe just about cotyledons was left. In the second method, the seedlings were maintained under vernalization for thirty days at 5-10&deg;C in a dark room. The results showed that the seedlings submitted to the first method recovered rapidly with normal emission of now shoots. The same was not observed for the seedlings from the second method which developed slowly and still anomalously

USING LINEAR TREND MODELS TO ANALYZE POLICY IMPACT

Policy researchers have become increasingly familiar with a number of improved techniques for analyzing data obtained from interrupted time-series designs for evaluating public programs and policies. In this paper we contribute to this trend by presenting two groups of data analysis techniques which are not currently widely used by policy researchers, but are likely to be valuable adjuncts to traditional regression techniques for analyzing data obtained from interrupted time-series designs. First, aids for model specification are presented that enable the analyst to define an appropriate linear trend model-often one which will reduce the degree of multicollinearity and, therefore, produce more precise estimates of the impacts of a public program or policy. Next we consider approaches for point estimation and joint (simultaneous) interval estimation of a policy intervention's total effect at various points in time. Copyright 1987 by The Policy Studies Organization.