Scientific Inquiry and Experimental Design
Core Concepts
A candidate must distinguish hypothesis (a testable, falsifiable prediction) from theory (a well-supported explanatory framework) and law (a descriptive regularity). Know the parts of an experiment: independent variable (what the experimenter manipulates), dependent variable (what is measured), controlled variables (held constant), and control group (baseline with no treatment). Understand randomization, replication, sample size, and blinding (single- and double-blind) as tools against bias. Recognize the difference between a correlation and a causal claim, and between a model and the system it represents.
Traps
Questions often swap independent and dependent variables, or present a "control group" that actually receives the treatment. Watch for confounds: a second variable that changes alongside the independent variable. Another trap is a conclusion that overreaches the data, such as generalizing from one trial or claiming causation from an observational study. Also distinguish repetition (same setup repeated) from replication (independent repetition, ideally by others).
Rule of Thumb
For any experiment, write the sentence: "Changing ___ (independent) causes a change in ___ (dependent), while ___ is held constant." If you cannot fill all three blanks, the design is incomplete.
Worked Example
A student tests whether fertilizer affects plant height, giving one group fertilizer and another plain water, but keeps the fertilized plants in a sunnier window. The independent variable is fertilizer; dependent is height; the sunlight difference is a confound, so any height difference cannot be attributed to fertilizer. Fix: place all plants under identical light.