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The design of an investigation study is the general plan of the investigator to obtain the answer to a raised question, that is to verify the investigation hypothesis. The selection of the type of design depends on the objective of the study, the resources on which count the investigator, the scope where to the results and the ethical requirements will be applied. All clinical test is based on the experimental method. The objective of this type of studies is to so obtain data on way medicines that it is possible to evaluate and to compare his effectiveness and security in one or more groups of individuals. In the studies that are carried out in a group of patients to those who he himself drug is administered to them, can be established criteria to change a medicine by another one or to change the doses (studies of phase I and 11) and of this form to evaluate the differences between different drugs or different doses from a same drug. Generally in the pharmacoclinics studies two or more groups of compare themselves to whom different treatments are administered to them. The simplest design consists of two groups of patients, a group that receives the drug in investigation and another group that receives placebo or the best one of the treatments available for the disease in study. The results of both treatments are compared and the differences settle down. The allocation of the treatments to each one of the groups is made in randomized form, that is at random. This means that the volunteers can be assigned at random to a group of treatment by means of numbers generated by a computer, applying a table of random numbers or, simply, removing the names from a hat. Of this form it is avoided that the subjectivity of the investigator takes part in the process of allocation of the treatments to the patients and allows that each patient counts on the same possibilities of being assigned to one or another group of treatment. Therefore, it can be assumed that the identified factors that can take to confusion are not identical in both groups and that the groups only defer to each other in which concerns the drug in investigation. If the allocation of treatments is not made in randomized form (for example when it is assigned according to the date of birth, number of clinical history of the patient, day from the visit to the doctor’s office, availability of bed or another strategy that allows the investigator to know the allocation before obtaining the consent of the patient) can happen a misalignment in the allocation of treatments and take place a slant. Slant to the confusion or involuntary alterations in the results of a study is denominated. The controlled studies include a called group of reference group control. The group control is a group of patients to whom a treatment is administered to him against which they compare so much the effectiveness as the security of the new drug in study. The existence of the group control allows to compare, to establish causality and statistical meaning. The election of the group control is fundamental. Ideally all clinical test must have a group placebo (medication that does not contain any active drug) like control since it allows to the unequivocal demonstration of the effectiveness and security of a medicine. Nevertheless, for ethical reasons, due to the existence of treatments for most of the diseases, not always placebo in the group is used control. - The group control can be:

1)Placebo .

2)Active Comparator or medicine pattern, is the best existing treatment until the moment for the disease in study .

3)Historical Control, are registries of answers to devices or obtained drugs before an investigation study begins. The historical control only must be used in exceptional cases, like very rare diseases, that they do not allow reuniting a sufficient number of patients or for the drug study that is used in the treatment of lethal diseases like cancer or AIDS.

Methodology:

In this section, I will describe in detailed :

l) The variables that will be evaluated in each clinical study and the form to measure them.

2) The design of the study .

3) Techniques and procedures that are going away to use to reach the proposed objectives.

4) The procedures to safeguard the security of the patients during the study and when finalizing his participation.

1) The variables:

In a clinical study the characteristic to study is named variable.

For example, when the effects of a drug study on the arterial pressure, the values of arterial pressure are the variable in study. We can say that the variables are properties that are not equal in all the individuals but that, like the name say, vary from an individual to another one.

It is sufficient that between different individuals from a population, a property can admit 2 possibilities (values) different so that at least it is considered variable. For example, if the population of the study is “men and women with slight arterial hypertension not treated” the property sex, it is a variable because it can at least adopt 2 different values.

But if the population of the study is “women with slight arterial hypertension treated” the property sex does transform itself into constant because there is no more two different properties and it stops being a variable.

When the variable describes the intervention made by the investigator and the cause of a certain action is considered denominates independent variable. The variable that it describes the result produced by the intervention it denominates dependent.

For example, we suppose that we want to study the factors of risk of anti-inflammatory the secondary digestive hemorrhage to the nonsteroid administration. In this example the investigator administers anti-inflammatory to the patients. The consumption of anti-inflammatory (dose, time of administration) is the independent variable. The appearance of digestive hemorrhage (if it appears) is the dependent variable of the received medication. The variables can be classified in:

,/Variable in study: those on which information in the study looks for and can be deduced of the specific objectives. For example the digestive hemorrhage in the previous example.

,/Variable irrelevant: those that do not have relation with the problem in study. For example the color of eyes of the individuals that participate in 16 clinical study of the previous example .

/Variable to control: those that without being the variables in study, have relation with the created problem and can modify the results of the investigation. For example, in the mentioned study, above the patients who take medicines that also act on the gastric mucosa or protecting it or damaging it .

Once defined the variables in study he must determine itself that measurement scales will be used to measure them, that is that assigns a value to them. The possible values can be numbers or names. The variables are denominated quantitative when they are moderate with representative fractions because the values are numbers that maintain an order and a magnitude and mathematical operations like adding can be made with them, reducing, to multiply or to divide As examples of numerical variables we can mention the values of arterial pressure or the values of hemoglobin.

The variables are called ordinal when the possible values follow a sequence that goes of greater to minor (or vice versa). The ordinal variables can be names (hipoglucemia slight, moderate or severe) or numbers (degree IV of Cardiac Insufficiency determined by the NYHA). The qualitative variables are those that are moderate with nominal or categorical scales because the values are names for example sex or race. The measurement scale that will be used for a variable determines the person who designs the protocol and depends on the precision whereupon she is needed to measure variable happiness based on the design of the study and the availability of the suitable instrument. For example, an investigator can decide to measure the variable glucemia in mg/I, being a this quantitative variable. But, if for the study that carries out, as much detail is not necessary and wants to only register if the individuals are hiperglucémicos severe or no, changes the measurement scale to noun and the variable will be qualitative. It is important to consider that if a variable can be measured in a quantitative scale must become this way, since when choosing a nominal scale loses information.

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