Investigators conducting a study regarding the effects of water pollution and pe

Question

Investigators conducting a study regarding the effects of water pollution and peptic ulcer disease obtained the following data:

A population of 9,000 men and women, aged 45 years, were examined on January 1, 1985. Of these people, 6,000 were exposed to toxins in the local water supply and 3,000 were not. At the time of this examination, 90 cases of peptic ulcer disease were discovered; 60 of these cases were among those exposed to toxins in their local water.

All the people at the initial examination who were free from peptic ulcer disease were followed with repeat exams throughout 1985. All repeat exams were completed on December 31, 1985. This study revealed 268 new cases in the total group; of these, 238 cases were among those exposed to toxins in their local water.

1.) Calculate the prevalence per 1,000 people of peptic ulcer disease on January 1, 1986 among the exposed. Be sure to review the dates for the denominator of the prevalence!

2.) Calculate the prevalence per 1,000 people of peptic ulcer disease on January 1, 1986 among the non-exposed.

3.) Calculate the 1985 incidence rate per 1,000 people of peptic ulcer disease among the exposed.

4.) Calculate the 1985 incidence rate per 1,000 people of peptic ulcer disease among the non-exposed.

Explanation / Answer

Please find the answers and calculations below:

Part 1) Calculate the prevalence per 1,000 people of peptic ulcer disease on January 1, 1986 among the exposed

Answer: The total number of individuals found infected at least once from peptic ulcer disease due to toxic water consumption between january 1985 to december 1985 will be the number of individuals already infected on january 1 1986.

Thus, the number of individuals actually infected during 1 January 1985 and 31 December 1985 due to toxic water and peptic ulcers is : 60+238 or 298.

The total population studied during this time is : 9000 individuals

Thus, the prevalance of disease on January 1 1986 = 298/9000 or 0.0331

Part 2) Calculate the prevalence per 1,000 people of peptic ulcer disease on January 1, 1986 among the non-exposed

Answer: The total number of individuals present on 31st December with peptic ulcer but not exposed to toxic water is : 30+30 or 60

The total number of individuals studied is 9000

Thus the prevalance of non-exposed individuals is 60/9000 or 0.0066

Part 3) Calculate the 1985 incidence rate per 1,000 people of peptic ulcer disease among the exposed.

Answer: The total number of incidences of peptic ulcers in 1985 is 268+90 or 358

The total population is 9000

Thus the total prevalance of peptic ulcer in 1985 is 358/9000 or 0.039

Part 4.) Calculate the 1985 incidence rate per 1,000 people of peptic ulcer disease among the non-exposed

Anwer: The total number of individuals non-exposed but with peptic ulcers in 1985 is 30+30 and the total population is 9000

Thus, the prevalance of non-exposed peptic ulcer disease is 60/9000 or 0.0066.

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