Batteries We work for the Watchdog for the Consumer consumer advocacy group. Weve been asked to look at a battery company that claims its batteries last an average of 100 hours under normal use. There have been several complaints that the batteries dont last that long, so we decide to test them. To do this, we select 16 batteries and run them until they die. They lasted a mean of 97 hours, with a standard deviation of 12 hours. a) One of the editors of our newsletter (who does not know statistics) says that 97 hours is a lot less than the advertised 100 hours, so we should reject the companys claim. Explain to him the problem with doing that. b) What are the null and alternative hypotheses? c) What assumptions must we make in order to proceed with inference? d) At a 5% level of significance, what do you conclude? e) Suppose that, in fact, the average life of the companys batteries is only 98 hours. Has an error been made in part d? If so, what kind?

Statistics for Psychology Concept 2 * z-test * single sample t test * used to compare a sample mean to a population with known mean, but the variance of the population is unknown * dependent means t test * also known as a “repeated measures” or “within subjects” research design because it compares two scores for each individual in the sample * Looks for a before and after effect * frequently seen in determining efficacy of a particular therapy or medication on a group of individuals * “before” scores as a baseline prior to a treatment * “after” scores gathered following a treatment or intervention (a dependent variable manipulation) * after minus before * unknown population mean and variance * two scores for each