# How can I fix the residual plot though transformation

What transformation can I use to fix this residual plot (make the red line horizontal). I tried square root, log, 1/y, and squared. None of them helped.

The data is of a 2 way ANOVA: Response Variable = time (in minutes) to teach a chimp a sign. Number of observations = 4 x 10 = 40

1. Response variable = time (in minutes)
2. Factor 1 = Sign (10 levels)
3. Factor 2 = Chimpanzee (4 levels)

Time, Sign, Chimp

178              1         1
60              2         1
177              3         1
36              4         1
225              5         1
345              6         1
40              7         1
2              8         1
287              9         1
14             10         1

78              1         2
14              2         2
80              3         2
15              4         2
10              5         2
115              6         2
10              7         2
12              8         2
129              9         2
80             10         2

99              1         3
18              2         3
20              3         3
25              4         3
15              5         3
54              6         3
25              7         3
10              8         3
476              9         3
56             10         3

297              1         4
20              2         4
195              3         4
18              4         4
24              5         4
420              6         4
40              7         4
15              8         4
372              9         4
190             10         4

• It's impossible to tell. Could you explain what the variables mean, give some brief summaries of the data characteristics, and tell us what you are trying to accomplish? – whuber May 10 at 21:39
• Nonaparametric smoothing regression? – Alexis May 10 at 21:41
• @whuber just edited in the data set – rabito May 10 at 21:47
• By default, you ought to consider analyzing logarithms of response times, as Fechner's Law suggests. – whuber May 10 at 23:15

The log transformation does not look bad:

Further, the log transformation is fairly clearly indicated by $$\lambda=0$$ within the Box-Cox family of transformations: