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409 pages, Kindle Edition
Published September 17, 2020
A fire alarm provides a good analogy for the types of hypothesis testing errors. Ideally, the alarm rings when there is a fire and does not ring in the absence of a fire. However, if the alarm rings when there is no fire, it is a false positive, or a Type I error in statistical terms. Conversely, if the fire alarm fails to ring when there is a fire, it is a false negative, or a Type II error.
You learned that we do not accept the null hypothesis. Instead, we fail to reject it. The convoluted wording encapsulates the fact that insufficient evidence for an effect in our sample isn't proof that the effect does not exist in the population. The effect might exist, but our sample didn't detect it-just like all those species scientists presumed were extinct because they didn't see them.
Finally, I admonished you not to use the common practice of seeing whether confidence intervals of the mean for two groups overlap to determine whether the means are different. That process can cause you to overlook significant results and miss out on important information about the likely range of the mean difference. Instead, assess the confidence interval of the difference between means.
P-values indicate the strength of the sample evidence against the null hypothesis. If it is less than the significance level, your results are statistically significant.
This is because it is the probability of observing a sample statistic that is at least as extreme as your sample statistic when you assume the Null Hypothesis is correct,.
P-values are the probability that you would obtain the effect observed in your sample, or larger, if the null hypothesis is correct. In simpler terms, p-values tell you how strongly your sample data contradict the null. Lower p-values represent stronger evidence against the null.
If the p-value is less than or equal to the significance level, you reject the null hypothesis and your results are statistically significant. The data support the alternative hypothesis that the effect exists in the population. When the p-value is greater than the significance level, your sample data don't provide enough evidence to conclude that the effect exists.