Using Residuals to Make Conclusions

I was recently given an assignment to analyse the residuals for 4 days of the following data. After plotting the residuals, what does this tell me about my data? I'm a bit confused with the context. Thanks.

I found the residuals by subtracting the observed value from the overall mean of the data (predicted value).


Active Member
Do not understand your plot. Which software did you use? Please use some standard statistical package to produce a boxplot for the distribution of residuals in each group. Then see if the distribution is symmetric, fat-tailed, unimodal, etc. If you are performing data analysis using a statistical method requiring normality of residuals (e.g. ANOVA F-test), check whether the residuals are normally distributed (via Kolmogorov-Smirnov test, Shapiro-Wilk test, etc).
Thanks for the reply. I used matlab for the residual plot and did it manually using number of bacteria - predicted number of bacteria (mean) for each day. This is a boxplot for the data. Boxplot.jpg


Active Member
So analyze the plot for the distributional properties I mentioned (symmetry / asymmetry, tails, etc). To check unimodality, you may use histograms.