1, based on the purpose and hypothesis of the study: If there are clear experimental groups and control groups in the study, the number of cases in each group can be determined according to the purpose of the study and the need to verify the hypothesis. The number of experimental group and control group will be set equal or close.

2. Determine according to the sample size: The total sample size has been determined, and the number allocated to each group can be determined according to the size of the sample size and the number of experimental elements. For example, if the total sample size is 200, in order to study three elements, the samples can be divided into four groups, with 50 in each group. This needs to consider the balance of sample size in each group.

3. Determine according to clinical experience or references: You can refer to the research design of similar clinical trials and determine the number of cases in each group according to experience. You can also refer to the sample size estimation method provided by medical statistics related reference materials to determine the sample size of each group. This requires full consideration of the differences in research conditions and objectives.

4. Determine by ANOVA: The study needs ANOVA, so the sample size of each group can be determined according to the requirements of ANOVA. Each group needs at least 30 cases, and the total sample size is at least 150 ~ 200 cases, so as to ensure the accuracy of the analysis of variance results. Variance analysis also needs to consider the requirements of freedom.

5. Carry out correlation analysis and judgment: To carry out correlation analysis, it is also necessary to ensure that there are at least 30 to 50 cases for each variable and at least 100 to 150 cases between two variables, so as to get accurate correlation coefficient. This can also be used as a reference to determine the number of cases in each group.