Two-Factor ANOVA

Two-Factor ANOVA

Harley (2003) examined effects on growth of the red algae Mazzaella parksii, which forms lawn-like growths in the intertidal region. He focused on two factors: (1) location and (2) herbivore abundance. The two locations were in areas along the shoreline below where this algae normally occurs (Low zone) and in areas along the shoreline where this algae does normally grows (Mid zone). For herbivore abundance, he had areas where limpets (Lottia species) were removed (Absent) and areas where limpets were not removed (Present). Harley then measured the area covered by Mazzaella (in cm²) for each replicate plot, and obtained the following data (NOTE: 0.5 has been added to each value to remove any zeroes from the data):

Height	Herbivores	Area	Height	Herbivores	Area
low	absent	88.46	mid	absent	0.50
low	absent	1188.02	mid	absent	622.54
low	absent	2178.41	mid	absent	2168.20
low	absent	276.96	mid	absent	0.50
low	absent	594.26	mid	absent	26.42
low	absent	1470.77	mid	absent	38.20
low	absent	1140.90	mid	absent	2204.33
low	absent	3732.72	mid	absent	524.36
low	absent	1257.14	mid	absent	377.49
low	absent	2132.08	mid	absent	1378.88
low	absent	1254.00	mid	absent	201.56
low	absent	627.25	mid	absent	9.92
low	absent	0.50	mid	absent	467.03
low	absent	1689.11	mid	absent	276.96
low	absent	1307.41	mid	absent	2073.96
low	absent	1746.44	mid	absent	2297.80
low	present	143.44	mid	present	0.50
low	present	209.42	mid	present	1037.23
low	present	0.50	mid	present	1230.44
low	present	64.12	mid	present	307.59
low	present	0.50	mid	present	38.98
low	present	0.50	mid	present	170.15
low	present	763.91	mid	present	657.09
low	present	1847.76	mid	present	1332.54
low	present	9.92	mid	present	1407.94
low	present	69.62	mid	present	2095.95
low	present	0.50	mid	present	401.05
low	present	16.99	mid	present	99.46
low	present	0.50	mid	present	7.57
low	present	1294.05	mid	present	1610.57
low	present	12.28	mid	present	1665.55
low	present	7.57	mid	present	2012.69

A)  Use a two-factor ANOVA to analyze these data and interpret your results. The data are not currently set up correctly for doing a two-factor ANOVA in Excel, so you will likely need to rearrange them!

B)  Test these data to see if (1) they are normally distributed and (2) the groups have equal variances.