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Question
Researchers at the National Weather Center in Portland, Maine have recorded the number of days where the temperature reached 90° (or above) in each year since records were first kept, starting in 1875. The number of 90° days forms roughly a normal distribution, with a mean of μ = 9.6 days/year that had a high temperature of 90° or higher. To see if this data showed any evidence of climate change (and specifically global warming), they also computed the mean number of 90° days for the most recent n = 4 years and obtained a mean number of 90° days per year for the past four years of x̅ = 12.25 days, with a standard deviation of s = 1.90. Using a one-tailed test with α = .05, the researchers completed the calculations, but they need your in drawing an appropriate conclusion. ( *Note: According to their calculations, the estimated standard error is s x̅ = 0.95.) Using the same one-tailed test (α = .05), determine if the data indicate that the past four years have had significantly more 90°+ days than would be expected for a random sample from this population. Write your conclusion in a sentence as it might appear in a research report (i.e., as you did in some of your most recent homeworks…don’t worry about it being perfect, just be sure that you write the results in sentence form). At the end of your sentence, be sure to include the test statistic ( t calculated ), the p-level ( α ), and a measure of effect size (estimated Cohen’s d ) (you’ll have to calculate Cohen’s d first).
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