# PH 302 California State University San Marcos Math Problem Set

The following scenario is the information necessary to answer questions 1-12.

SCENARIO: 1236 Marine recruits entered training during one week in June. Marine recruits are medically examined and must be injury and illness free before beginning training. 112 refused to participate in a study to follow them during 12 weeks of training for the development of stress fractures. All recruits who consented to participate (everyone but those who refused to participate) were successfully followed for all 12 weeks. During the 12 weeks, 55 recruits developed a stress fracture. Of these 55, 26 subjects suffered stress fractures in the first 6 weeks and each of these 26 were fully recovered within 5 weeks. The shortest recovery time among those suffering stress fractures after week 6 was 7.5 weeks. At the beginning of training it was determined that 20% of participants were classified as being in “poor physical fitness.” The remaining recruits were in “better than poor physical fitness.” The incidence of stress fractures in the poor physical fitness group was 9.8%.

Hint: you may want to “draw” a timeline of the 12 week follow-up period to better understand prevalence and incidence of stress fractures over that time period.

1. What is the size of the study group?
2. What is the stress fracture incidence?
3. What is the stress fractures incidence rate?
4. What is absolute risk of stress fracture during training?
5. What is the prevalence rate of stress fractures at the beginning of training (1st day of training)?
6. What is the prevalence rate of stress fractures at the end of training?
7. Create a 2X2 table for stress fracture given physical fitness group?
8. What is the incidence rate of stress fractures among the better than poor physically fit recruits?
9. What PERCENT of stress fractures in the poor fit group could be reduced by increasing fitness to better than poor?
10. Among all recruits, what percent of stress fractures could be reduced by increasing fitness to better than poor?
11. What is the relative risk for stress fracture if a recruit is in poor fitness?
12. What is the interpretation of this relative risk?

The following scenario is the information necessary to answer questions 13-19.

SCENARIO: In National City they have begun a new initiative to reduce the effects of risky sexual behavior among the 150,000 residents. 33% of the population is between 1-14 years old, 20%, 15-21 years old, 30%, 22-40 years old, and 17% older than 41. Chlamydia is the most common sexually transmitted disease with a duration that can vary from a few days to many months. Before the program began, 145, 15-21 year olds were diagnosed with chlamydia in 1996. 145 people aged 22-40 were also diagnosed with chlamydia in the same year. 16 people aged 15-40 died from chlamydia in 1996. A total of 345 people of all ages were diagnosed with chlamydia during 1996.

In 1997 a sample of 3500 National City residents were recruited into a study . Each subject was asked about their current sexual behavior and each person’s medical record was reviewed for diagnosis of chlamydia at the time of enrollment in 1997. 37 individuals from the sample had documentation of chlamydia of which 35% claimed to never use condoms during the same time period. Condom use in the entire sample was reported by 62% of the subjects.

13. What was the crude prevalence rate for chlamydia for 1996 in National City?

14. What was the age-specific chlamydia rate for 15-21 year olds in National City in 1996? For 22-40 year olds?

15. What age group seems to have the highest problem with chlamydia, 15-21 or 22-40?

16. What is the chlamydia case fatality rate for 15-40 year olds in 1996?

17. Fill in the 2X2 table for chlamydia vs condom use in the sample in 1997?

18. Does condom use appear to be associated with chlamydia diagnosis in the 1997 study? Yes or no.

19. Was there a positive or negative association of condom use with chlamydia diagnosis?

USE THIS DOCUMENT FOR SUBMITTING ANSWERS: (I attached a file for the answers)

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