Hello!

I have measurements (length and volume) of fish collected in two years. I
want to know if the the relationship between length and volume is the same
for both years. The number of fish measured is different for each year. I
don't know whether lm or aov is more appropriate to use.

Here are the two output options:

Call:
lm(formula = Volume ~ Length * Year)

Residuals:
     Min       1Q   Median       3Q      Max
-1.35062 -0.42695 -0.02234  0.29789  1.78540

Coefficients:
                  Estimate Std. Error t value Pr(>|t|)
(Intercept)      -8.699125   0.543372 -16.010   <2e-16 ***
Length            0.151462   0.006708  22.578   <2e-16 ***
Year1         1.627903   1.168158   1.394   0.1660
Length:Year1 -0.024259   0.014510  -1.672   0.0972 .
---
Signif. codes:  0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1

Residual standard error: 0.6016 on 119 degrees of freedom
Multiple R-squared: 0.8384,     Adjusted R-squared: 0.8343
F-statistic: 205.8 on 3 and 119 DF,  p-value: < 2.2e-16

----
AND for aov:
----

               Df  Sum Sq Mean Sq  F value    Pr(>F)
Length          1 219.457 219.457 606.4349 < 2.2e-16 ***
Year          1   2.970   2.970   8.2073  0.004934 **
Length:Year   1   1.012   1.012   2.7952  0.097173 .
Residuals     119  43.064   0.362
---
Signif. codes:  0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1


Thanks very much for any help.
Kirsten

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