Investigators in the Netherlands conducted a study to investigate the prevalence incidence and mortality of chronic obstructive pulmonary disease

Investigators in the Netherlands conducted a study to investigate the prevalence incidence and mortality of chronic obstructive pulmonary disease

Question 1.  Investigators in the Netherlands conducted a study to investigate the prevalence, incidence, and mortality of chronic obstructive pulmonary disease (COPD) in the general population (Afonso A, Verhamme K, Sturkenboomand M, Brusselle G.  COPD in the general population: Prevalence, incidence and survival. Respiratory Medicine, 2011).  The study was conducted within the Integrated Primary Care Information database, a longitudinal observational database that started in 1992 and contains patient data from computer-based medical records while patients are receiving care from participating physicians throughout the Netherlands.  The source population comprised 185,325 men and women aged 40 or older while they were enrolled in the database.  The study started on January 1, 2000, and all patients were followed for (1) development of COPD from study entry until COPD diagnosis, removal from the database, or July 1, 2007; and (2) occurrence of COPD-related death from study entry until death, removal from the database, or July 1, 2007.

 

These data are abstracted from the paper:

 

  Population at baseline on January 1, 2000 No. prevalent cases at baseline on January 1, 2000 No. incident cases during follow-up Person-years of follow-up at risk for COPD
All Participants 185325 5595 1713 596,460
Males 89697 3158 995 284,286
Females 95628 2437 718 312,174

 

  1. Calculate the point prevalence of COPD among (1) all participants, (2) males, and (3) females at baseline on January 1, 2000. (5 pts)

Prevalence                        = # existing cases/total population

PrevalenceAll                            = 5,595/185,325                             = 0.030 (3.0%) on January 1, 2000

PrevalenceMales                 =

PrevalenceFemales              =

  1. Summarize your results in 1-2 sentences. (5 pts)
  2. Calculate the cumulative incidence of COPD among (1) all participants, (2) males, and

(3) females from January 1, 2000 – July 1, 2007. (5 pts)

Cumulative Incidence    = # new (incident) cases/total population at risk 

CIAll                                                   = 1,713/(185,325 – 5,595) = 1,713/179,730

= 0.0095 (0.95%) over the study period from Jan 1, 2000 – July 1, 2007

CIMales                                  =

CIFemales                               =

  1. Summarize your results in 1-2 sentences. (5 pts)
  2. Calculate the incidence rate of COPD per 1,000 PY (1) all participants, (2) males, and (3) females during the study period. (5 pts)

Incidence Rate  = # new (incident) cases/person-time contributed by population at risk

IRAll                     = 1,713 cases/596,460 PY            = 0.002872 cases/PY                 = 2.9 cases/1,000 PY

IRMales           =

IRFemales         =

  1. Summarize your results in 1-2 sentences. (5 pts)

Question 2.  A population of 100 healthy women was recruited from the internal medicine practice at UMC from June 1 – June 30, 2000 and followed for the development of breast cancer.  Twelve women developed breast cancer after each was followed for 4 years.  Ten women who remained healthy were followed for 2 years and then were lost to follow-up.  Five women died of heart disease after 6 years of follow-up.  These 5 women did not develop breast cancer. The remaining women remained healthy and were each followed for 10 years.

  1. Calculate the cumulative incidence of breast cancer in this population and interpret your result in 1-2 sentences. (5 pts)

Cumulative Incidence    = # new (incident) cases/total population at risk

CI                                         =

  1. Calculate the number of person-years of observation that was accrued by this population.

(5 pts)

  1. Calculate the incidence rate and interpret your result in 1-2 sentences. (5 pts)

Incidence Rate  = # new (incident) cases/person-time contributed by population at risk

IR                                   =

  1. Which measure of disease incidence – cumulative incidence or incidence rate – is more appropriate in this situation? Why? (5 pts)