4. Mrs. Smith is participating in a clinical trial. She started treatment on Mar

Question

4. Mrs. Smith is participating in a clinical trial. She started treatment on March 3, 1999 and is expected to have a folow-up visit every 6-months for the next three years. (a) Create a vector of the dates when Mrs. Smith is expected to show up for her follow- up visit . (b) Mrs. Smith showed up on the following dates, enter these dates into R as Date objects 9/10/1999, 2/10/2000, 9/16/2000, 2/23/2001, 99/2001 3/28/2002 ) It is unrealistic to expect Mrs. Smith to show up on the dates from part (a). However, did Mrs. Smith have a folow-up appointment within three weeks of each expected follow-up date?

Explanation / Answer

The detailed r code for all the parts is as follows :

# dates for schedule appointements

shd.dates<- seq(as.Date("1999/9/3"), by = "6 months", length.out = 6)
shd.dates<- as.Date(shd.dates,"%m/%d/%Y")

# dates of arrival as given in the question

arr.dates<- (c("9/10/1999", "2/10/2000", "9/16/2000", "2/23/2001","9/9/2001","3/28/2002"))

arr.dates<- as.Date(arr.dates,"%m/%d/%Y")

# combine to form a data frame
df<- cbind.data.frame(shd.dates,arr.dates)

# difference in week of the 2 dates, 3 instances where the follow up happened within 3 weeks

diff_in_weeks = difftime(arr.dates,shd.dates, units = "weeks")
diff_in_weeks

Hope this helps

We first entered the dates and then using the seq function created a vector of scheduled appointments , then calculated the difference between the scheduled and the arrival date in weeks to answer part 3 . If the difference is less than 3 then the appointment happened within 3 weeks else not .

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