Biostatistics Questions

1. A cohort study is conducted to assess the association between clinical characteristics and the risk of stroke. the study involves n= 1250 participants who are free of stroke at the study start. Each participants is assessed at study start (baseline) and every year thereafter for five years. the table below displays data for hypertension.

Hypertension at baseline and two years later

                                                                        Two years later: Not hypertensive                       Two Years later: Hypertensive

Baseline: Not hypertensive                                                                850                                                                    148

Baseline: Hypertensive                                                                       45                                                                      207

status measured at baseline and hypertension status measured two years later.

a) compute the prevalence of hypertension at baseline

b) compute the prevalence of hypertension at two years.

c) Compute the cumulative incidence of hypertension over two years.

Question 2 : Hypertension at baseline and stroke five years later                                                                         

                                                                               Free of stroke at five years                          Stroke

Baseline: Not hypertensive                                                               952                                       46

Baseline: Hypertensive                                                                     234                                       18

The data shown above were collected in the study described in problem 1 relating hypertensive status measured at baseline to indicate stroke over five years.

a) Compute the cumulative incident of stroke in this study.

b) Compute the cumulative incidence of stroke in patients classified as hypertensive at baseline.

c) Compute the cumulative incidence of stroke in patients free of hypertension at baseline.

d) Compute the risk difference of stroke in patients free of hypertension.

e) Compute the relative risk of stroke in patients with hypertension as compared to patients free of hypertension.

f) Compute the population attributable risk of stroke due to hypertension.

A national survey is conducted to assess the association between hypertension and stroke in persons over 75 years of age with a family history of stroke. Development of stroke is monitored a over 5- years follow- up period. The data are summarized below and the numbers are in the million.

Hypertension and the Development of stroke

                                                                               Developed Stroke                    Did not develop stroke

Hypertension                                                                     12                                                  37

No hypertension                                                                  4                                                  26

a) Compute the cumulative incidence of stroke in persons over 75 years of age.

b) Compute the relative risk of stroke in hypertensive as compared to non-hypertensive persons.

C) Compute the odds ratio of stroke in hypertensive as compared to non-hypertensive persons.