Epidemiological Exercises
1. In a hospital 50 cases of E.coli diarrhoea were confirmed by culture of stool samples out of 150 samples. Same samples were also subjected to microscopy and following were findings:
| Dysentry present | Dysentry absent | Total | |
| Test + ve | 30 | 10 | 40 |
| Test – ve | 20 | 90 | 110 |
| 50 | 100 | 150 |
(1) Find out sensitivity and specificity of direct microscopy as a diagnostic test for E. coli diarrhoea.
(2) What is Positive Predictive Value and proportion of false positive in the microscopy?
2.There are 200 students in a nursery standard of school. 10 days back a student Parth in the class suffered from fever with rashes and was diagnosed as a case of measles. Now 50 students are suffering from measles. On taking history all students from parents 24 gave history of measles in past and 75 were vaccinated against measles. Find out secondary attack rate.
3. . In a cohort study among smokers following were the findings.
| No. of cigarettes smoked / day | Lung Cancer | Total population |
| <5 | 10 | 10,500 |
| 5 – 15 | 17 | 7,500 |
| 15 – 30 | 20 | 7,000 |
| >30 | 30 | 6,500 |
| None | 2 | 12,000 |
Comment on relative risk of cigarette smoking for causation of carcinoma of lung.
4. Relationship between cigarette smoking and C.H.D.
| Smoking category | No. of cases of CHD | Person years of observation |
| Never smoked | 7 | 4000 |
| Ex-smoker | 6 | 2000 |
| Current Smoker | 15 | 3000 |
| Total | 28 | 9000 |
- Comment on given tabular data
- What is meant by ‘cessation experiments’? Explain the same in relation to above data.
5. In a survey of 200 patients suffering from fever 70 showed positive blood smear for plasmodia. All 200 patients were also subjected to dipstick test and test come positive in 50 patients. Out of these who showed negative blood smear 20 showed positive dipstick test. Comment on ‘Yield’ of dipstick test for diagnosis of malaria.
6.In a PHC having 30,000 populations, 3000 blood smears were examined in the year 2003. The microscopic examination showed 300 cases positive for malaria. During the same period there were 60 confirmed deaths due to malaria out of total 300 deaths. Calculate different rates and ratios.
7.A study was conducted among 761 employees of Ahmedabad city working in various section of AMC during March to August 2004.
| Smoking Category | Chronic Bronchitis | Total | |
| Yes | No | ||
| Smoker | 72 | 200 | 272 |
| Non Smoker | 58 | 431 | 489 |
| Total | 130 | 631 | 761 |
Comment on the given table.
8.Self Reporting Questions (SRQ) were tested for screening of blind persons to detect psychiatric morbidity. All SRQ positive and negative subjects were again examined by qualified psychiatrist for finding out psychiatric morbidity. The results are as under.
| SQR results | Psychiatrist’s Diagnosis | Total | |
| Morbidity Present | Morbidity Absent | ||
| Morbidity Positive | 55 | 11 | 66 |
| Morbidity Negative | 11 | 123 | 134 |
| Total | 66 | 134 | 200 |
- Find out the Sensitivity and Specificity of the test.
- Find out the Positive Predictive and Negative Predictive Value of the test.
- What is blinding?9. Comment on the given table.
Type of assistant Rural % (n = 1092) Urban % (n = 229) Doctor 40.8 92.3 Trained nurse 41.4 6.7 Trained Birth Attendant 6.3 0.5 Relative / others 11.4 0.5 Nobody / Don’t know 0.2 –
10. In the study of knowledge about symptoms of dengue following were the findings.
| Symptoms | Rural(n = 284) | Urban(n = 318) | Total(n = 602) | |
| 1 | Fever | 236 (83.0) | 290 (92.0) | 526 (87.4) |
| 2 | Bleeding | 77 (27.1) | 132 (41.5) | 209 (34.7) |
| 3 | Headache | 68 (24.0) | 142 (44.5) | 210 (34.9) |
| 4 | Body ache | 53 (18.7) | 139 (44.0) | 192 (31.9) |
| 5 | Rashes | 22 (7.7) | 66 (20.8) | 88 (14.6) |
| 6 | Others | 27 (9.5) | 28 (8.8) | 55 (9.1) |
Study the giver tabulate data and comment.