Randomisation sampling

Carefully randomised samples of breast milk obtained from women residing in the upper and lower Michigan peninsula (U.P., L.P.) were examined for PBBs. All samples were derived from deliveries occurring during August 1976. Ninety-six percent of the U.P. women (51/53) and... 

Sample numbers have been randomised to minimise regional bias, help separate false from true anomalies and obtain meaningful estimates of the variance of duplicates. Field duplicates, analytical duplicates, in-house standards and certified reference materials are introduced at regular intervals in the analytical streams. 

Do you randomise your samples in an analytical run (including duplicates). Section 5 Method validation... 

This equation illustrates the importance of the size of the sample in relation to the size of the particles. In an incompletely randomised material, s2 will be greater, and in a completely unmixed system, indicated by the suffix 0, it may be shown that ... 

In one sense moving from the sample to the population in this way is a leap of faith However, it should work providing the sample is representative of the complete population. If it is not representative, but if we can assume that the treatment difference is homogeneous across the population as a whole, then we would still obtain a valid estimate of that treatment difference. It is the randomisation that protects us in this regard. 

Finally note that in our considerations we have worked with groups of equal size. It is straightforward to adapt the calculations for unequal randomisation schemes and the computer packages mentioned earlier can deal with these. Altman (1991), Section 15.3 provides a simple method for adapting the standard sample size calculation to unequal group sizes as follows. If N is the calculated sample size based in an equal randomisation and k represents the ratio of the number of patients in one group compared to the other group, then the required number of patients for a A to 1 randomisation is ... 

So for example, if a 2 to 1 randomisation is required and 200 patients would have been needed for an equal allocation then the revised sample size is ... 

As with sample size in superiority trials we generally power on the basis of the per-protocol set and increase the sample size to account for the non-evaluable patients. This is particularly important in non-inferiority trials where the full analysis set and the per-protocol set are co-primary analyses. Note also, as before in superiority trials further factoring up may be needed if there are randomised patients who are being systematically excluded from the full analysis set, as is the case, for example, in anti-infective trials. 

Five months into the trial (388 patients randomised) another study showed that the effectiveness of nevirapine was related to the minimum concentration and so a fourth arm was added nivarapine twice dally (N2). Randomisation was now to Nj, E, Nj - -E and N2 in the ratio 1 2 1 2. The final sample size was 1216 and in the final analysis, data from both periods... 

If repeated samples are taken from the same population it is unlikely that they all will have identical characteristics, either to each other or the population. This is a consequence of the randomisation process and the variability in the... 

Efficient sampling really boils down to selecting small quantities such that they are truly representative of the much larger whole. The necessity for sheets to be representative of batches and for batches to be representative of the formulation is self evident. The direction of test pieces relative to the axes of the sheet and randomisation of their position in the sheet are also important if the sheet cannot be guaranteed homogeneous and isotropic. 

The. sip-file resulting from the randomise sequence command holds the names of all mutants in the sample population. Since these names contain the randomized positions as well as the substituted amino acids, they can be used to derive the distribution of amino acids for certain positions. By analyzing this distribution for the subset of nondestabilized mutants, it is possible to gain hints about amino acid preferences. 

Fig. 2. Numerical example showing that a non-randomised structural default (heterogeneous zone between sample nos. 11-14) cannot be cleared by increasing sample size either by a factor 2 (top case) or 3 (bottom case).

This routine calibration (curve adjustment) is performed for every reagent carrier lot. A total of 30 tubes is drawn from the beginning and the end of every sealed lot role and randomised. 2-4 reagent carriers each are measured by five different instruments with each of the 15 calibrators, so that 10-20 reflectance values are obtained. These values enable calculation of the regression with the help of the functional curve that is best suited for the test. Plotting the functional curves is part of the manufacturing process. Final release of the new lot is effected only after testing with control samples (human material) in the control laboratory. 

Initially, 12 sub-samples of oil B with a concentration of 2.03mgl 1 Cl solvent red 24, 0.996 mg l-1 quinizarin and 2.40 mg l-1 Cl solvent yellow 124 were analysed. The extraction stage was carried out in two batches of six on consecutive days. The markers in all 12 sub-samples were quantified in a single HPLC run, with the order of the analysis randomised. This study was followed by the analysis, in duplicate, of all 15 samples. The sample extracts were analysed in three separate HPLC runs such that the duplicates for each sample were in different runs. For each HPLC run a new standard and a fresh batch of mobile phase was prepared. 

Although the two-period crossover design has certain intrinsic weaknesses, intra-individual variation is usually smaller than variation between subjects, and bioequivalence can usually be established using a smaller number of subjects in a crossover study. The order in which subjects receive single doses of the different formulations must be randomised and an adequate interval allowed between doses to ensure washout. The number of subjects will depend on the variability of the kinetics of the compound. A power calculation should be performed using historical data, if possible. In practice, the minimum number of volunteers needed is 12 and the maximum usually about 24 but is occasionally more. The number and times of blood samples is a critical a sufficient number of samples is required around the to permit and to be identified with adequate accuracy. Sampling should continue for at least 3-4 half-lives and later samples should be spaced so that no more than about 15% (or ideally 10%) of the AUC has to be determined by extrapolation or interpolation between points. Model-fitted data are usually not acceptable should be obtained directly from the observed concentration data and... 

Sometimes a trend is detected between the vials a systematic increase or decrease in the content of an element or substance appears between vials. Two explanations are possible. Either the production of the material has suffered from a drift or the measurement method has itself drifted. To differentiate between both reasons, the analyst must perform the measurements between samples in a non chronological manner. As samples should be taken regularly during the packaging procedure and are labelled it is possible to arrange their analysis in a randomised way. If a random selection is performed for the between bottles test the drift in production may be overlooked. Figure 4.8 illustrates the differences in conclusion in case of production and method drift. It indicates that in addition to the dispersion of the results, the analyst must also identify the evolution of the results in terms of absolute quantity. 

A bulk sample of a paramagnetic substance contains a multitude of individual magnetic moments arising from the individual molecules in the sample. The tendency of these to align with an applied magnetic field will be in competition with the randomisation of their orientations... 

Takahashi et al. [1965TAKAVES2] and Westmm et al. [1965WES/TAK2] have measured the low-temperature heat capacities of two samples of the dicarbide, with compositions of ThCi 9s(cr) and ThCi 93(01) respectively. The former sample probably contained some free carbon, but the consistent values of ((298.15 K) - S (() K)) of (68.6 + 0.3) J K mol from the two studies has been taken to refer to the ThCi.94(cr) composition. The assumption that this phase contains randomly mixed C and C2 groups then gives a randomisation entropy of (ThQ 94, cr, 0 K) = (1.9 + 0.3) J-K -mol, to give ... 

Special studies such as randomised control clinical trials or observational studies can be used to gather data that are not collected by routine monitoring systems these however involve additional costs and it may prove very difficult to maintain them consistently over a long period. Sentinel reporting systems, which collect data on a carefully selected sample, are useful for monitoring the short-term impact of policy implementation, particularly in order to detect unexpected or unintended outcomes [18]. Time pressures, the availability of financial resources and the willingness of staff members to comply with requirements will influence the type of monitoring method selected. 

Observation of the sensory expert panellists ways of working makes the flavourists also aware that each piece of sensory descriptive information must always be linked to the set of products that was evaluated within a sensory test. Sensory scores of intensity are relative to the context of the product space and must not be taken as absolute scores. Indeed, even if the contrast and convergence effects (Amerine et al., 1965) are minimised by the balanced or randomised order of presentation of the samples in every sensory test, they are never totally eliminated. 

---