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# Confounding Variables

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Is there a difference in mean needle length between the two species?
How to get rid of confounding variables?

Pine A out of 35 needles the mean is 7.66 inches
Pine B out of 35 needles the mean is 10.64 inches

Pine A : 7.75, 7.10, 8.05, 8.40, 6.50, 7.90 7.55, 8.55, 7.40, 8.55, 6.10, 7.05, 8.10, 6.25, 5.90, 7.60, 7.25, 8.00, 7.60, 6.95, 7.00, 7.05, 6.10, 6.85, 7.15, 8.55, 5.65, 8.00, 6.70, 6.55, 6.00, 5.65, 6.50, 8.10, 7.65

Pine B : 12.15, 12.05, 10.40, 12.00, 12.00, 11.90, 11.50, 12.05, 10.50, 10.00,12.15, 11.80, 12.10, 11.40, 11.25, 11.40, 11.80, 11.95, 12.00, 11.10, 9.95, 11.80, 12.00, 11.85, 10.95, 11.20, 9.25, 10.90, 10.60, 12.00, 11.00, 11.45, 9.85, 11.90, 9.80

1. present raw data graphically for each species
2. data summarized graphically for each and labeled
3. trends visible and explained
4. mean needle lengths for both displayed on comparative graphs with error bars
5. state appropiate sample size and implications
6. conduct test of statistical significance comparing the length of both
- hypotheses (null and alternative)
- give equation used and degree of freedom
- give P value and interpretation
7. give 90% confidence interval for each species mean individually
- give equation used and degree of freedom
- give the 2 confidence intervals and meaning
8. conclusion of the study

##### Solution Summary

Is there a difference in mean needle length between the two species?
How to get rid of confounding variables?

Pine A out of 35 needles the mean is 7.66 inches
Pine B out of 35 needles the mean is 10.64 inches

Pine A : 7.75, 7.10, 8.05, 8.40, 6.50, 7.90 7.55, 8.55, 7.40, 8.55, 6.10, 7.05, 8.10, 6.25, 5.90, 7.60, 7.25, 8.00, 7.60, 6.95, 7.00, 7.05, 6.10, 6.85, 7.15, 8.55, 5.65, 8.00, 6.70, 6.55, 6.00, 5.65, 6.50, 8.10, 7.65

Pine B : 12.15, 12.05, 10.40, 12.00, 12.00, 11.90, 11.50, 12.05, 10.50, 10.00,12.15, 11.80, 12.10, 11.40, 11.25, 11.40, 11.80, 11.95, 12.00, 11.10, 9.95, 11.80, 12.00, 11.85, 10.95, 11.20, 9.25, 10.90, 10.60, 12.00, 11.00, 11.45, 9.85, 11.90, 9.80

1. present raw data graphically for each species
2. data summarized graphically for each and labeled
3. trends visible and explained
4. mean needle lengths for both displayed on comparative graphs with error bars
5. state appropiate sample size and implications
6. conduct test of statistical significance comparing the length of both
- hypotheses (null and alternative)
- give equation used and degree of freedom
- give P value and interpretation
7. give 90% confidence interval for each species mean individually
- give equation used and degree of freedom
- give the 2 confidence intervals and meaning
8. conclusion of the study

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