Table 1.

Means and opportunities for selection calculated for growth rates of clones free of mutations (F) and contaminated with mutations (M)

Pair compared	Sample sizes		Mean growth rates, 1/h		df†	t′(B−A)	Opportunity for selection, ×100		df†	t′(B−A)
A* vs. B*	A	B	A	B			A	B
F30 vs. M30	127	229	0.418	0.417	254.1	−0.083	0.380	0.714	353.9	2.211
F38 vs. M38	143	266	0.247	0.200	244.9	−7.448**	5.266	9.926	386.7	3.884**
F30 vs. F38	127	143	0.418	0.247	210.1	−31.84**	0.380	5.266	145.9	7.238**
M30 vs. M38	229	266	0.417	0.200	433.9	−47.74**	0.714	9.926	275.7	9.178**

^** indicates probability of the type I error lower than 0.001. Critical values of t′ were calculated for four planned comparisons. 

^*A and B serve as variables that should be substituted within each row for appropriate F or M assayed at 30°C or 38°C. 

^† Degrees of freedom are not natural numbers because they were calculated according to Welsh's procedure to compensate for unequal sizes and variances of the compared samples (19).