Exercise 6.284 describes a study to examine the effects of tea on the immune system. Use the information there to test whether mean production of interferon gamma as a response to bacteria is significantly higher after drinking tea than before drinking tea. Use a 5% significance level.

Data from Exercise 6.284

Drinking tea appears to offer a strong boost to the immune system. In a study introduced in Exercise 3.82 on page 203, we see that production of interferon gamma, a molecule that fights bacteria, viruses, and tumors, appears to be enhanced in tea drinkers. In the study, eleven healthy non-tea-drinking individuals were asked to drink five or six cups of tea a day, while ten healthy nontea- and non-coffee-drinkers were asked to drink the same amount of coffee, which has caffeine but not the L-theanine that is in tea. The groups were randomly assigned. After two weeks, blood samples were exposed to an antigen and production of interferon gamma was measured. The results are shown in Table 6.23 and are available in ImmuneTea. The question of interest is whether the data provide evidence that production is enhanced in tea drinkers.

Table 6.23

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20 Tea 11 47 5 13 55 18 48 52 56 58 11 Coffee 3 15 16 21 21 38 52