The article “Antimicrobial Activities of Essential Oil of Eight Plant Species from Different Families Against Some Pathogenic Microorganisms” (Res. J. Microbiol. 2016: 28–34) reported on an experiment in which various concentrations of eight essential oils were applied to active bacterial cultures. The accompanying table shows the inhibition percentage of E. coli for each oil-concentration combination.

a. Perform a two-factor ANOVA, testing both main effects at the .01 level.
b. Apply Tukey’s method to the eight essential oils, and describe what you find.

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Oil Type Ginger Thyme Coriander Marjoram Mustard Chamomile Licorice Nigella 2 60 58 57 17 14 22 10 15 Concentration (µL/mL) 8 92 86 89 51 4 72 64 63 34 31 36 14 29 6 80 78 81 49 45 54 23 42 63 63 28 48 10 99 96 99 67 70 72 33 57