Question

A study is done to compare the fuel efficiency of cars. The first group of cars generally get about 38 miles per gallon. The second group of cars generally get about 24 miles per gallon. Based on the mean values of each​ group, what inference can be​ made? What else might a person conclude from the mean​ values?
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Part 1
Which of the following is a correct inference based on the mean​ values?
A.The cars in group 1 generally are more fuel efficient.
The cars in group 1 generally are more fuel efficient.
B.The cars in group 1 and group 2 are equally fuel efficient.
The cars in group 1 and group 2 are equally fuel efficient.
C.The cars in group 2 generally are more fuel efficient.
The cars in group 2 generally are more fuel efficient.

Answer 1

Answer: A. The cars in group 1 generally are more fuel efficient.

Additional points a person might conclude or should consider from the mean values:
- The average difference is 38 − 24 = 14 mpg in favor of group 1, so on average group 1 gives substantially better fuel economy.
- This is an inference about averages only — it does not mean every car in group 1 outperforms every car in group 2. Individual values may overlap.
- You cannot tell from the means alone whether the difference is statistically significant or how precisely it is estimated. You need sample sizes, standard deviations and/or a confidence interval or a two‑sample test to assess uncertainty.
- Means say nothing about distribution shape or outliers; check histograms or boxplots and variances.
- Causation cannot be assumed from mean differences alone — there may be confounders (different car types, driving conditions, maintenance, etc.).

Recommended next steps: compute standard deviations, sample sizes, a 95% confidence interval for the mean difference and/or perform a two‑sample t‑test, and examine the data distributions and study design for potential confounding.