Experimental Design and Laboratory Methods: Controls, Replication, and Validation
Core concepts
Understand the architecture of a sound experiment: a clear hypothesis, an appropriate control (negative, positive, vehicle, sham), randomization, blinding, biological versus technical replication, and pre-specified analysis. Know common techniques and what they actually measure-PCR and qPCR, gel electrophoresis, western blotting, ELISA, microscopy and fluorescence, flow cytometry, chromatography, mass spectrometry, and sequencing. For each, know the purpose of key reagents (primers, antibodies, dyes, ladders, standards) and the major sources of artifact (contamination, nonspecific binding, antibody cross-reactivity, batch effects).
Traps
Items often reward recognizing the missing control: a western blot without a loading control, an ELISA without a standard curve, a PCR without a no-template control. Confounding variables-different handlers, times, or instruments between groups-are frequently hidden in the scenario. Another trap is confusing technical replicates (same sample measured repeatedly) with biological replicates (independent samples), which inflates apparent n and false confidence.
Worked rule of thumb
For any proposed experiment, ask three questions in order: What is the comparison, and is the only difference the variable of interest? What result would falsify the hypothesis? Could a plausible artifact produce the same result? If you can name an artifact that mimics the predicted outcome, a control is missing and that is likely the intended answer.
Study strategy
Practice critiquing short method descriptions for confounds and absent controls, and always state what each technique can and cannot conclude.