Main effect of treatment

We will return to the example where we have just a single baseline variable, size of primary tumour, predicting the outcome, time to disease recurrence, but now in addition we have randomised the patients to one of two treatment groups, test treatment and placebo. 

A formal comparison of the two treatments could be based on the unpaired t-test, comparing the mean time to disease recurrence in the test treatment group with the mean time to disease recurrence in the control group. While this is a valid test, it may not be particularly sensitive. The separation between the two groups is clear, but if we now simply read off the times to disease recurrence on the y-axis we will see considerable overlap between the groups we will have lost some sensitivity by ignoring the size of the primary tumour variable. 

Consider an alternative approach applying simple linear regression to the data from these two groups of patients. The equations of these lines can be written  

Had the treatments been equally effective then the points in the placebo group would not have been, in general, below the points in the test treatment group. 

The lines would be co-incidental with = 02- Indeed the larger the treatment difference the bigger the difference between the two intercepts, and a2- Our main interest is to compare the treatments and within this framework we compare the values of Ui and U2 through the null hypothesis Hg Ui = U2 and the alternative hypothesis a a2- The signal is provided by the estimate of — U2 and the noise is the standard error of that estimate we compare the signal-to-noise ratio to t 3 to give the p-value. 

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When using such a statistical significance test, it is important to recognise that this generally has low power in a trial designed to detect the main effect of treatment/... 

For binary data in multi-centre trials we will have a series of 2 x 2 tables, one for each of the centres. For categorical and ordinal data with c categories, we will have a series of 2 x c tables. The CMH test in the first instance provides a single p-value for the main effect of treatment. 

We call these equations (or models), main effects models. In the next subsection we will be adding to the main effects (of treatment and the covariates), treatment-by-covariate interaction terms. 

In my view, if we wish to retain this single label treatment effect and use the model with interaction, the only sensible approach is to regard the model with interaction as an elaboration upon the model without. In other words, the main effects of treatment and stratum must be as they would be without the interaction and the interactions must be described as a departure from this position. This is effectively the type II philosophy. The reader will perhaps appreciate that there are deep waters here and that the ICH E9... 

The main effect of treatment is achieved in the first 10 min after engaging of the sorbents and the model solution. The time of reaching sorption equilibrium for both cellulosic sorbent and carbonate rocks with the dye is 30 min and further increase of contact time is unreasonable. 

Data were analyzed using GLM procedure of SAS (SAS Institute Inc., 2009) considering the main effects of treatment and age and their interaction. 

Numerous and complex mechanisms are reported in literature for soil solarization effects, involving also the combination of several interrelated processes (Katan 1987 Stapleton and DeVay 1995 Stapleton 1997), but main effects of solarization treatments were found related essentially to the thermal action of solarization and the consequent chemical and biological changes occurring in the soil. 

The effects of treatment at 15-50°C on some of the characteristics were studied by Evans et al (4) using laboratory reactors. These were fed semi-continuously, with feed intervals of 5-20 min, and DO was maintained at about 20% of saturation. The treatment conditions were thus similar to the high DO treatments used in the present study, but the main difference was that Evans etal s 3 and 15 litre reactors were smaller than those used in the present study by factors of 167 and 33 respectively. Evans etal s expression for TS and COD take the form ... 

The main effect of the surface treatment is the removal of the native defect containing surface on the fibers. This surface layer itself can not sustain any great degree of... 

While for an accurate (+1%) treatment of the rototranslational spectra (v = v = 0) the matrix elements (vj (9 v f) of the lower rotational states do not much depend on the rotational transitions (j,f), for the vibrational bands (v > 0), for v f v, relatively strong j,f dependences are usually observed (9 designates the multipole and polarizability operator. Similar j dependences are also obtained for the dipole components Bc that are significant for line shape computations [63]. The accounting for the j dependences is relatively easy because the main effect of the j dependence is on the integrated intensity, but not so much on the shape of the profile. The main effect of neglecting the j dependence in the low-temperature spectra is an excess intensity of the Sj(l) lines. 

The interactions of dietary fat and protein on the promotion phase of breast carcinogenesis were examined by feeding weanling rats a control diet (16% of kcal from protein and 24% of kcal from fat) for 4 weeks and subsequent assignment to the 9 dietary treatments following DMBA administration. As in the combined phase study we observed no protein by fat interactions or main effects of... 

Data represents main effects of each nutrient from a 3 x 3 factorial experiment with 40 rats per diet and 120 for main effects. The rats were fed a common diet until DMBA administration at which time they were assigned among the 9 diets for an additional 28 wk. The 9 diets (3x3 factorial) were fed for 4 weeks, from weaning until DMBA administration. Following DMBA treatment all rats were fed a common diet. 

The main purpose of this chapter is to describe methods of modifying polyolefin surfaces in such a way as to render them printable, and also to describe the tests that are available for determining the effects of treatment and... 

Retinoids in Cancer Prevention and Treatment Since the discovery of vitamin A, the observation that the main effects of deficiency are hyperplasia and loss of differentiation of squamous epithelium has raised speculation that the vitamin may he associated with carcinogenesis. Either deficiency may be a risk factor for cancer or increased intake may be protective. Deficient animals develop more spontaneous tumors and are more sensitive to chemical carcinogens, whereas liver reserves of vitamin A are lower in patients with cancer than in controls. One of the genes repressed by retinoic acid is the myc-oncogene. 

Individually, the cholinesterase inhibitors improve memory in patients with AD. There have been no head-to-head comparisons made of the drugs to determine w hether one is more effective than the others and no trials of agents in combination. The main know n differences are the side effect profiles, titration schedules and the dosing regimens (Table 39.1). The most common side effects of treatment with cholinesterase inhibitors are gastrointestinal and include nausea, vomiting and diarrhea. A meta-analysis of the efficacy and safety of these agents revealed that despite many clinical studies show ing... 

Provider policies determine who can provide the benefits of the vouchers and under what conditions. They are important for three of the main aims of subsidy schemes, for different reasons. For health gain, provider policies make it possible to select providers with the highest technical quality and therefore the greatest effectiveness of treatment. For technical efficiency, the policies affect how much the scheme costs. For patient satisfaction, a free provider participation strategy can be used that allows patients to decide whom to see. 

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