A multiweek laboratory experiment is described, which guides students to use data to make decisions through multiple steps, before reaching a final conclusion. The lab focuses on the comparisons of fluorescence and absorbance spectroscopies to determine the concentration of a desired substance in an unknown sample in consideration of a complex matrix. Students use pooled class data to draw conclusions on the sensitivity, selectivity, dynamic range, and detection limits of the different types of spectroscopy techniques and instrumentation. After determining the concentration of the substance by both an absorbance and fluorescence method, students must statistically evaluate their results from the two methods and perform standard additions to quantify their analyte in the presence of the matrix effects. Students are prompted with questions to answer but are provided limited procedural information to engage and grow students' critical thinking and problem-solving abilities. It is anticipated that the experiment can be implemented or modified for an "Instrumental Analysis" or "Quantitative Analysis" type of analytical chemistry course.