جستجوی مقالات مرتبط با کلیدواژه "حجم نمونه" در نشریات گروه "پزشکی"

Before interventional clinical studies in humans, researchers usually perform preclinical studies in vitro or in vivo to evaluate the initial efficacy, toxicity, and pharmacokinetics of interventions. Sample size determination in animal studies is necessary both in terms of correct and scientific inference and in terms of ethics. Therefore, the purpose of this paper is a brief description of how to determine the sample size in a study on laboratory animals.

One of the concerns in research design is to determine the sample size and sampling method. This is because the volume of the sample is reduced due to reduced accuracy and the additional sample size also increases the cost. Usually the researcher has to select a sample from the community in which to calculate the mean or ratio. Factors such as the dispersion of the studied trait, statistical errors and the accuracy of the measurements are effective on the sample size required. The basis for calculating the sample size for a research is its specific objectives. Specific goals can be descriptive or analytical. For descriptive purposes, the researcher wants to estimate the average of a quantitative trait or the percentage of a qualitative trait. For analytical purposes the researcher wants to compare the mean of the quantitative variable or the ratio of the qualitative variable in the two societies. Statistical formulas or tables or software are used to calculate the sample size, which practically all have the same mechanisms. In the present article, these issues are briefly described.

Backgound and Nowadats, it is very common to investigate the effect of a new method or medicine by using a comparison between two independent groups in many clinical studies, but unfortunately the sample size part has not been done based on scientific formulas but on practical issues in some researches of this type of cinical studies, and this makes some unreliable results. Therefore, this paper studies how to obtain the sample size for binary data when the research aim is to compare two independent groups, and some tables are prepared to reach this aim.
In this applied study, how to obtain the sample size for binary data to compare two proportions is studied. Chi-square test and exact Fisher test as well as chi-square test with yates correction are used in this paper, and some formulas and tables are presented to the aim of calculating the sample size with the significant level of 0.05 and power of 80% and 90%. SAS 9.2 is used to obtain the sample size in different scenarios.
Findings: Some applied and medical examples are presented to get familiar with the right way of obtaining the sample size, and it is argued how to use the formulas and tables to calculate the minimum size of an appropriate sample.
it is strongly suggested to use the formulas and tables presented at this paper to obtain the appropriate sample size in such researches that their study plan is based on the comparison of two independent groups with binary data.

One of the important strategies for preventing and controlling cardiovascular diseases (CVD) is providing training through interventions at the population. This study aimed to explain the sample size and sampling structure of the Isfahan Healthy Heart Program (IHHP). This program was considered as a comprehensive community-based interventional trial to modify population lifestyle in relation to cardiovascular disease (CVD) and its risk factors prevention and control. Isfahan Healthy Heart Program (IHHP) addressed four target groups including adults, health professionals, patients with cardiac diseases, and children and adolescents in three districts in Iran including Isfahan and Najaf Abad (intervention) and Arak (reference). It was consisted of three phases: baseline survey in 2000-2001, intervention in 2002-2005 and post-intervention survey in 2006-2007. Four evaluation studies were done during 2002 to 2005 to evaluate knowledge and behaviors improvements. The sample sizes and sampling methods in the pre- and the post-intervention phases were as followed: 12514 and 9572 and quota, stratified, cluster, random, probability proportionate to size, systemic and simple random in adults; 1946 and 1992 and quotas, stratified, cluster, random, probability proportionate to size, simple random, simple random in adolescents; 923 and 2015 and simple random in health professionals; and also 814 and 502 and simple random in patients with cardiac diseases. We carried out a 10-year longitudinal cohort study entitled the Isfahan Cohort Study on population aged ≥ 35 years starting from the baseline to examine the incidence of cardiovascular disease events and to calculate the risk assessment chart for cardiovascular disease occurrence. Isfahan Healthy Heart Program, as comprehensive community-based interventional trial in Iran, was so similar to the same worldwide.

Sampling in qualitative and quantitative research are very different، because it aims، gaining a deep understanding of the phenomenon is being investigated، rather than generalizing the results. Participants Selection in the qualitative study is done with aim of achieve the maximum information about the phenomenon under study. In quantitative research there is too much emphasis on a random selection، an equal chance for selection of all members of the research community، but in the qualitative study samples or participants are selected or invited. Purposive sampling that also is called purposeful or qualitative sampling that means purposeful selection of samples for acquiring knowledge or information. This type of sampling does not focus on developing the fixed and immutable rules or generalizing the results but try to better understand the phenomenon in special field. Purposive sampling consists of three main types including «Sampling to Achieve Representativeness or Comparability»، «Sampling Special or Unique Cases» and «Sequential Sampling». Saturation in qualitative research as a method of sampling is considered the gold standard. In this paper، we tried to introduce the participant’s selection methods and the differences between quantitative and qualitative method and the strategy for decision making about data saturation will be offered.

Sample size calculations are now mandatory for many research protocols and it is a mainquestion before accomplishing a research. This paper outlines the ways of calculatingsample sizes in clinical trial studies with two groups: binary, ordered categorical, andcontinuous outcomes. In each section a table for calculating sample size and workingexamples are given.

For each and every graduate student the process of composing a thesis is the center part of training and education in research methodology. The content of such material becomes important when the research study turns into a manuscript which is submitted for publication in a journal of medical sciences. Deficiencies and drawbacks in terms of research methodology in student theses still remains a controversial issue. Due to lack of sufficient information concerning the accuracy of research methodology in student theses, the purpose of this study was to evaluate the accuracy of research methodology in several aspects of student theses including: research variables, study population, sample size, sampling method and associated factors. The research was conducted on student theses in Islamic Azad University, school of Dentistry in 2007-2008. All presented theses from 09/23/2007 to 09/21/2008 in Islamic Azad University, Dental Branch were evaluated in this descriptive study. Based on 13 variables, aspects such as research variables, study population, sample size and sampling method were assessed for accuracy and classified into 3 categories (correct, relatively correct and incorrect). Information regarding associated factors including student specifications, related department and head researcher… were collected and entered into a data sheet. Each thesis was assessed for accuracy as follows: "correct: if more than 75% of variables were correct"; "relatively correct: if 50-75% of variables were correct"; "incorrect: if less than 50% of variables were correct". The role of associated factors was determined using chi-square statistical test. 137 student theses were evaluated. The rate of inaccuracy in research methodology of research variables, study population, sample size and sampling method was found to be 40.2%. Failure to justify the sample size was seen in 71% of the cases, incorrect organization of data sheet was reported in 53%, and not stating all the variables including new and compound variables was seen in 37% of theses. This study indicated that there are significant drawbacks in student theses which mandate proper steps to be taken to reduce the level of inaccuracies in research methodology. This will not only improve the validity of the research itself but will also provide reliable results to be applied to general population.

For each and every graduate student the process of composing a thesis is the center part of training and education in research methodology. The content of such material becomes important when the research study turns into a manuscript which is submitted for publication in a journal of medical sciences. Deficiencies and drawbacks in terms of research methodology in student theses still remains a controversial issue. Due to lack of sufficient information concerning the accuracy of research methodology in student theses, the purpose of this study was to evaluate the accuracy of research methodology in "materials and methods" part of student theses and associated factors. The research was conducted on student theses in Islamic Azad University, Dental Branch in 2007-2008.

All presented theses from 09/23/2007 to 09/21/2008 in Islamic Azad University, Dental Branch were evaluated in this descriptive study. The materials and methods aspect of the theses were assessed for accuracy based on 15 variables and classified into 3 categories (correct, relatively correct and incorrect). Information regarding associated factors including student specifications, related department and head researcher… were collected and entered into a data sheet. Each thesis was assessed for accuracy as follows: "correct: if more than 75% of variables were correct"; "relatively correct: if 50-75% of variables were correct"; "incorrect: if less than 50% of variables were correct". The role of associated factors was determined using chi-square statistical test.

137 student theses were evaluated. The rate of inaccuracy in research methodology of materials and methods was found to be 30.6%. Not reporting the reliability of the instrument measurement was seen in 79% of the cases. 71% of the authors failed to justify the sample size and 25% used incorrect statistical tests for data analysis.

This study indicated that there are significant deficiencies in methods and materials section of student written theses which requires proper steps to be taken to reduce the level of inaccuracies in research methodology. This will not only improve the validity of the research itself but will also prevent erroneous results from being presented to the public.

Sample size estimation is one of the crucial issues in the research methodology in medical sciences. It is an important issue for not only researchers but also readers of medical papers; their frequent questions show how much they need to simple but accurate information.This paper presents the basic concepts of sample size calculation, and simplifies complicated issues using concrete examples to clarify the concept of sample size estimation for none-professional readers in statistics. The paper starts with explaining the basic concepts of sample size calculation such as effect size, confidence interval and confidence coefficient, statistical errors, and assumptions in sample size calculation. Then, it presents the common formulae in the sample size calculation to estimate a mean, a proportion, to compare two means and to compare two proportions.

One faced to matched data when the main object for a study is investigation of the effect of a given factor on an outcome, such that the samples are matched on the some factors which are known as confounders. The response can be according to quantitative or qualitative scales. Matched case-control, before-after and crossover studies are used frequently in medicine. The significant tests are required to sufficient samples. In this paper, formulas for determination of sample size in matched studies are introduced by considering the scale of response and extended for matched case-control studies with multiple controls and illustrated using practical examples. Using statistical techniques, formulas for determination of sample size are introduced according to the scale of response. The practical examples interpreted in order to clarify the formulas and their applications. One can increase the power and the accuracy of the statistical tests for matched studies, using the introduced formulas.

One of the questions that most investigators specially physicians encounter when they plan a research project is determining sample sizes. Selecting a sample greater than what is required to obtain the desired results causes wastage of the sources, while selection of very small samples often leads the investigator to the results which have no practical use. Determining number ot the required samples depends on various factors such as type, purpose and domain of action of the study and expected results which all should be considered at the time of planning.
The present article deals with the cases that make it necessary to adopt a great smaple, and the cases that make selection of the samail smples more advisable. Anyway, in the cases that number of the samples is optionally selected, the percentge of problems appeared in research findings will increase and leads to wrong interpretaition or the results.
Meanwhile it should be taken into account that large number of samples cannot be a substitute for incorrect samplins plan.
In recent years, easier methods have been used to determine the required number of samples in addition to the formulas presented in the statistical texts. one of these methods is to prosper the tables and pamphlets that are published by WHO.
The presented tables and examples in the pamphletes are selected in such a way that contain many of the current methods in the health investigations. This not only has the direct practical application for the researchers but also opens a horizon toward the statistical methodology in determining number of the samples.