Understanding Person-Time Person-time refers to all the people in a study who are exposed to a medicine in a given amount of time. Person time can be measured in as person-months, person-years, or person-hours; it depends on the exposure of the drug. During a cohort study patients may be taking different amounts of a drug at various times. Person-months would be calculated by adding the total number of months each person is taking the drug over a given time. For example, patients A, B, and C were prescribed a drug over a six month period. In order to calculate the total exposure of the drug in the study, add the total number of months prescribed for each patient. The following diagram is an example of how to understand person-months after: Consider following diagram: Patient A: I---XXX---I---XXX---I---XXX---I---XXX---I-----------I-----------I 2 2 6 75 mg Patient B: I-----------I---XXX---I---XXX---I---XXX---I---XXX---I-----------I 1 2 10 10 Patient C: I---XXX---I-----------I---XXX---I-----------I---XXX---I----------I 75 mg 2 2 The above diagram represents data collected during a six month cohort study. Each interval, the blue boxes, represent a one month period. Imagine each interval represents a one month period. What would be the total exposure of the drug for all three patients over the six month period? In other words, what are the person-months for this study? To determine person-months, count up the total number of months each person was using the drug. Then add these values together to determine person months. In this case, the study was conducted over a six month period and involved three participants. Patients A and B used the drug for 4 months. Patient C used the drug for three months. Person-months = 4 + 4 + 3. Therefore, the total person-months for this study is 1nths. You can also calculate person-months per dosage using this information. For example, at a dosage of 2, it is 5 since a dosage of 2 was prescribed a total of 5 times for all participants in the six month study. Student DATA KEY 1
Materials: Student page Scenario cards Student Data Page activity InstrUCtions: 1. Handout the first set of scenario cards to each group. 2. Record the dosages for each person into the appropriate data table. 3. Calculate the total person months for each dosage and write it in the appropriate data table. 4. Repeat steps 1 and 2 for Part 2 using the 2 nd set of scenario cards. 5. Create a table to record the total person-months for each dosage. Record your data. 6. Answer the questions. 7. Create the data tables needed to complete Part 3. 8. Repeat steps 1, 2, and 3 for the 3 rd set of scenario cards. 9. Answer the processing out questions. Student DATA KEY 2
Scenario Card Activity 1 Adam Adam took aspirin in February (80mg), March (180mg), June (80mg) and October (160mg). Maria Maria took 160mg of aspirin April through July. In August & September she took 180mg of aspirin. Susan Susan took 100mg of aspirin October and November. Jason Jason took aspirin January (180mg), February (160mg), July (80mg), November (100mg), and December (80mg). Valerie In March, April, May, October and November Valerie took 80mg of aspirin. In December she took 100mg. Robert In April & May he took 180mg of aspirin. June and July he only took 80mg and in August & September he increased it by 80mg. Student DATA KEY 3
Scenario Card Activity 2 Fergie Fergie took aspirin during the months of January(500mg), February(500mg), April(660mg), July(660mg), September(820mg) and October(820mg). will.i.am Will.i.am took 500mg of aspirin in March, April, June, July and 980mg in November. Taboo Taboo recounted that he took 660mg of aspirin in May, June and December. Apl.de.ap Apl.de.ap took the most aspirin of everyone. He said that he remembers taking aspirin all year except for the month of May. During the first half of the year he took 660mg and 980mg the second half of the year. Autumn Autumn remembers taking 500mg of aspirin for the first three months of the year and 820mg the last three months of the year. Summer Summer would only take aspirin during the summer months of June-August. She started with 500mg the first month and increased her dose by 160mg each month. Student DATA KEY 4
Scenario Card Set #3 Bart Bart stated he liked playing video games the most. He definitely played on the weekend for at least 4 hours. During the school week he remembered that he had a football game on Tuesday and a school activity on Thursday. He knows that he did not play any video games on Monday. On Wednesday he thinks he played about an hour and on Friday he was excited because it was the weekend so he stayed up all night playing video games. He estimates that it was about 5 hours on Friday. Maggie Maggie said she was not into video games a lot and only liked to play for a little while. She didn t play on the weekend because her family was out of town to visit relatives. On Monday she was tired because it was the start of the school week so she didn t play anything. On Tuesday she played with her little brother for an hour. Her brother still wanted to play so on Wednesday she played with him for another hour. On Thursday she was too tired to play. On Friday her mom bought her a new video game so she ended up playing for about 3 hours. Lisa Lisa said that she liked playing video games but didn t always have time because of extra-curricular activities. Over the weekend she played for two hours. During the week she wanted to play more but was busy. On Monday she only got to play for an hour. On Tuesday she had to go shopping with her mom. On Wednesday she had projects to do at school so wasn t able to play. She remembered playing on Thursday and Friday at her friend s house. Her friend got two new games and they decided to play as much as they could. They played each video game for about two hours each day. Student DATA KEY 5
Activity 2A: Person Months Student Data Page Activity: 1 Six friends recorded the number of times they took aspirin for pain during the span of one calendar year. At the end of the year they got together to see what their results were. What would be the total number of person-months for each group at different dosages? In data table 1, record the dosage for each person in the appropriate month. Add the total number of months for each dosage to complete data table 2. Table1: Dosage of Aspirin Total person months = 27 Module 2A: Person Months Student Data Page Friends Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec. Adam 80 180 160 Susan 100 100 Jason 180 80 100 80 Maria 160 160 160 160 180 180 Valerie 80 80 80 80 80 100 Robert 180 180 80 80 160 160 * Teachers: due to size of answer boxes, students may or may not include mg as part of their answers. Table 2: Person-months per Aspirin Dosage Aspirin Dosage 8 10 16 18 Person-months 10 4 7 6 Student DATA KEY 6
Activity 2A: Person Months Student Data Page Activity: 2 Six different friends recorded the number of times they took aspirin for pain during the span of one calendar year. At the end of the year they got together to see what their results were. What would be the total number of person months for each group at different dosages? In data table 1, record the dosage for each person in the appropriate month. Add the total number of months for each dosage to complete data table 2. Table 1: Dosage of Aspirin Total person months = 34 Module 2A: Person Months Student Data Page Friends Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec. Fergie 500 500 660 660 820 820 Will.i.am 500 500 500 500 980 Taboo 660 660 660 Apl.de.ap 660 660 660 660 660 980 980 980 980 980 980 Autumn 500 500 500 820 820 820 Summer 500 660 820 * Teachers: due to size of answer boxes, students may or may not include mg as part of their answers. Table 2: Person-months per Aspirin dosage Aspirin Dosage 16 50 66 82 98 Person-months 0 10 11 6 7 Student DATA KEY 7
Analysis Questions for activities 1 and 2 1. What are the total person months for the amount of aspirin exposure for the entire study? Activity 1: 27 Activity 2: 34 Total Person months = 27 + 34 = 61 2. Which dosage has the most person months? 66 3. Which month(s) had the least amount of aspirin taken? Activity 1: February activity 2: May Combined: May 4. Which month(s) had the most amount of aspirin taken? Activity 1: April & May activity 2: July Combined: July 5. Why do you think the most aspirin was taken at this time of year? Answers may vary. Possible responses can include: hayfever, outdoor allergies, kids are outside playing/hiking/swimming and can be injured. 6. Would the data collected be a good representation of all middle school students? Explain. No. Explanations may vary but may include: Too small of a sample of kids; not enough information about the kids ages or size or activity level or allergies, etc. Activity 3 Teachers: Students need to construct a data table reflecting the time each person played video games Three friends got together to play video games. They wondered how many hours they spent playing games for the past week. They calculated how many person hours were spent playing video games. What would be the total number of person-hours for each person? What is the total number of person-hours for the group? Table 3: Person-Hours for Playing Video Games M T W Th F Weekend Bart x x 1 x 5 4 Maggie x 1 1 x 3 x Lisa 1 x x 2 2 4 Total person-hours 24 = (add up all hours played) Student DATA KEY 8
Analysis QUestions for Table 3 1. What are the total person-hours for each student? Person-hours for each person: Bart: 10 hours Maggie: 5 hours Lisa: 9 hours 2. Which person has the most person-hours for playing video games? Bart (10 hours) 3. Which day had the most amount of game playing? Friday 4. Why do you think this day had the most person-hours? School is out for the weekend and kids want to play; no kid wants to do homework on Friday night; kids need a break after going to school all week Processing out Questions 1. What is person-months? The actual number of months all people in the study received treatment or took medication. 2. What other ways can person-months/hours be applied in science? Answers may vary but can include: Determine the amount of time spent working on a lab experiment; determine the amount of time spent developing new medicines or treatments 3. What other ways can person-months/hours be applied to your life? Answers may vary: amount of time spent on homework; amount of time individual group members spend on a group project; amount of time spent on extra-curricular activities 4. Why would understanding person-months be important for scientists conducting medical research? Answers may vary: It would help scientists understand how effective their research is; It would help scientists understand the long term costs or benefits of the research; it would help researchers monitor progress Student DATA KEY 9