CODEWITHSUNDEEP
rconfidence-interval
greg gregory
greg gregory

Reputation: 11

How to calculate confidence interval

We are supposed to find the 90% confidence interval for a 74 year old man.

x <- c(58, 69, 43, 39, 63, 52, 47, 31, 74, 36) y <- c(189, 235, 193, 177, 154, 191, 213, 165, 198, 181) (where x is age and y is cholesterol level) i used: correlation <- cor.test(x, y, conf.level = 0.90)

and that gives me this:

data: x and y t = 1.2656, df = 8, p-value = 0.2413 alternative hypothesis: true correlation is not equal to 0 90 percent confidence interval: -0.1857867 0.7839057 sample estimates: cor 0.4084309

and when i asked people in my class what values they were getting all of them told me (203.2717, 205.5591) Where am I going wrong, the corr.test is telling me -0.1857867 0.7839057.

also the next portion of the assignment is asking us to calculate a 90% prediction interval for a 74 year olds, how would i do this in r studio? thanks a lot!

Upvotes: 0

Views: 445

Answers (1)

Merijn van Tilborg
Merijn van Tilborg

Reputation: 5897

df <- data.frame(
  x = c(58, 69, 43, 39, 63, 52, 47, 31, 74, 36),
  y = c(189, 235, 193, 177, 154, 191, 213, 165, 198, 181)
)

predict.lm(
  lm(y~x, data = df), 
  newdata = data.frame(x = 74), 
  interval = "confidence", 
  level = 0.90
)

#      fit    lwr    upr
# 1 204.42 178.99 229.85

Upvotes: 1

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