Problem 39E

The compressive strength of concrete is being tested by a civil engineer who tests 12 specimens and obtains the following data:

(a) Check the assumption that compressive strength is normally distributed. Include a graphical display in your answer.

(b) Construct a 95% two-sided confidence interval on the mean strength.

(c) Construct a 95% lower confidence bound on the mean strength. Compare this bound with the lower bound of the two-sided confidence interval and discuss why they are different.

Chapter 8: bivariate correlational research - When you see two things that are related, and you think are related, but actually have nothing to do with one another To be causal - Covariance - Internal validity - Temporal precedence Correlational strength - As you get a measurement change by this much on this chart or whatever - You get the same ratio change on the other chart for the other variable - This means that they are changing at the same rate o Either moving at the same amount in the same direction [perfect correlation o Or moving at the same amount in the opposite direction [perfect correlation - When they don’t move at the same rate; imperfect correlation – this is what r