Our test statistic is F =21.2, the p-value (.0003) is very small. There is very strong evidence of an interaction among the two factors in their...

Our test statistic is F =21.2, the p-value (.0003) is very small. There is very strong evidence of an interaction among the two factors in their effects on the mean GSI level. This is not surprising, the profile plots showed that the lines didn"t appear to be too parallel. What does a statistically significant interaction mean? It implies that the effect of temperature upon the mean GSI is different at the the various photoperiod levels. Similarly, the effect of photo-period upon the mean GSI index is different at the two temperature levels. If you detect an interaction, it usually doesn"t make much sense to continue along to test main effects because, by definition, these are not consistent - e.g. the effect of temperature is different at the two photo-periods. What to do if an interaction is present?