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LESSON PURPOSE: To master the methodology for calculating and using the correspondence criterion to determine the significance of the discrepancy between several compared groups of studied phenomena

LESSON METHODOLOGY: Students independently prepare for a practical lesson in the recommended literature and complete their individual homework. The teacher within 10 minutes checks the correctness of homework and indicates the mistakes made, checks the degree of preparation using testing and an oral survey. Then, students independently calculate the compliance criterion to determine the accuracy of the discrepancy between several compared groups of studied phenomena, evaluate the data obtained and formulate a conclusion. At the end of the lesson, the teacher checks the students' independent work.


1. When is the chi-square metric applied?

2. What is the calculation of the indicator? 2 based on?

3. What is the "null hypothesis"?

4. What are the steps involved in calculating the chi-square compliance criterion?

5. How is the number of degrees of freedom determined when calculating the compliance criterion?

6. How is the result of the compliance indicator evaluated?

7. When are differences between several compared groups evaluated as significant?


The reliability of differences and the relationship of phenomena with factors can be determined when calculating the compliance criterion. Correspondence criterion? 2 is used for statistical evaluation of the law of distribution of empirical variational series and for proving the significance of differences between two or more sample populations. The compliance criterion is applied when the research results are presented in absolute values ​​and the outcome has many gradations (recovered, discharged with improvement, worsening, died), and also if the subject has several signs (several age groups, several treatment methods). The criterion is based on the assumption (null hypothesis) that there is no difference between the values ​​obtained as a result of sample observation and theoretically calculated. The more actual values ​​differ from the expected ones, the greater is the certainty that the factor under study has a significant effect.

The compliance criterion is calculated by the formula

An example of calculating a compliance criterion. Stage 1 - we formulate the null hypothesis - the introduction of an influenza vaccine did not affect the incidence of influenza. In this case, the distribution of sick and not sick in the two observation groups should be the same and correspond to the final distribution.

Does influenza vaccine affect influenza incidence

It also calculates the expected values ​​for those who are ill and not ill with the flu from among those not vaccinated.


Task number 1. Calculate the compliance criterion? 2 and determine whether the difference between the numbers obtained in the process of statistical research and the “expected values” is significant or not significant.

Task 1

Determine if marital status affects student performance

Task 2

To establish whether participation in hostilities affects the incidence of post-traumatic stress disorders in military personnel

Task 3.

Determine whether ad media affects a patient’s decision to consult a dentist

Task 4.

To establish whether the presence of Helicobacter pylori infection affects the frequency of pre-tumor pathology and gastric malignancies

Task 5.

Determine whether the season affects the nature of weight changes in children

Task 6.

To determine whether the profession affects the prevalence of clinical forms of borderline mental disorders (PPR)

Task 7.

Determine whether age affects the use of sedatives and sleeping pills

Task 8.

To establish whether the nosological form of the disease affects the effectiveness of the use of demineralized bone implants in pediatric traumatology and orthopedics

Task 9.

To establish whether work experience affects the incidence of hypertension in teachers

Task 10.

To establish whether the health status of students studying in various faculties of medical universities is different

Task 11.

To establish whether the marital status affects the level of physical development of primary school children

Task 12.

To establish whether the thoroughness of the patient's recommendations of the doctor affects the nature of the course of gastric ulcer

Task 13.

To establish whether the acidity of gastric juice affects the blood condition in patients with gastric cancer

Task 14.

To establish whether fatness affects the mental development of the child

Recommended literature for students:

• Lisitsyn Yu.P. Social hygiene (medicine) and healthcare organization. Kazan, 1999, p. 307 - 308

• Serenko A.F., Ermakov V.V. Social Hygiene and Health Organization, M, 1984, p. 139 - 149.

• Yuryev V.K., Kutsenko G.I. Public health and healthcare. S-P, 2000, p. 197 - 199.

• Public health and healthcare. Ed. V.A. Minyaeva, N.I. Vishnyakova M. “MEDpress-inform.”, 2002. - p. 108-109, 113-114.

• Zaitsev V.M., Livland V.G., Marinkin V.I. Applied Medical Statistics. S.-P. The Tome, 2003.
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