Problem
Mission: You are studying how urbanization influences insect communities in big cities. You know that city parks can be very important places where native insects can thrive, despite being surrounded by inhospitable habitat. The parks in your city differ greatly in size and you want to know if this influences native insect diversity. You decide to test whether larger city parks harbor a higher diversity of native insects.
i. Describe an observational or experimental study that you would do to test this hypothesis, making clear how your study is based on the cause and effect. Did you describe an observational or an experimental study?
ii. What kind of statistical test could you use for this study? an ANOVA, or a regression/correlation?
TESTS
ANOVA
We use ANOVA (Analysis of Variance) when our independent variable (treatments or conditions being compared) is made up of classes or categories (discrete variables). ANOVA allows us to test for differences among our treatment groups. Our data are typically plotted as different bars in a bar chart, with error bars to show variation among replicates.
REGRESSION
We use regressions when our independent variable is a continuous variable. This analysis finds a line that best fits the relationship of the dependent variable with variation in the independent variable. We can test whether this line has a slope different from zero (is anything other than flat). We can also quantify how well the independent variable can predict the response (dependent variable) that we've measured (how well the data fit the line).