Confidence intervals 2.0

Question

A publishing company wanted to test whether typing speed differs when using word processor A or word processor B. A random sample of 25 typists was selected and the typing speeds (in words per minute) were recorded for each secretary when using word processor A and then when using word processor B. (Which word processor was used first was determined for each typist by a coin flip).

Based on the collected data, a 95% confidence interval for μ_d, the mean difference (word processor A - word processor B) was found to be (2.5, 7.8).

The appropriate hypotheses for testing whether the typing speeds differ when using word processor A or word processor B is 

 

 

Interpret the 95% confidence interval in context. Make sure that your interpretation quantifies the effect that the type of word processor used (the explanatory variable, X) has on the typing speed (the response variable, Y).

Check the answer to compare it against yours.

Please type up a reasonable response to this open ended question. 

Answer 1

The confidence interval does not contain 0, therefore with 95% confidence we can say the difference of population means being equal to 0 has a 5% or less chance of occurring. We can therefore reject the null hypothesis of zero difference at a significance level of 0.05.