About twenty percent of the GED Science test is scientific reasoning: designing experiments, reading them critically, and predicting what results would prove or disprove a claim. This is the highest-yield content on the exam because the rules are short, rigid, and identical from question to question. Learn three variable types, the shape of a fair test, and how conclusions relate to data, and roughly nine of the 46 questions answer themselves in seconds - no science memorization required.
The Three Variables
The independent variable is what the experimenter changes on purpose - the amount of light, the temperature, the type of fertilizer. The dependent variable is what gets measured to see the effect - plant height, reaction time, speed. The control or constant variables are everything deliberately held the same so the test stays fair: same soil, same water, same species. The GED asks these as definitions, as what-was-changed readings of a scenario, and as which-is-mismeasured logic problems. The giveaway for the independent variable is always the experimenter's choice; the giveaway for the dependent variable is the measuring instrument. If a question mentions a graph axis, the y-axis almost always carries the dependent variable.
What Makes a Test Fair
A fair test changes one variable while controlling everything else, repeats enough times to smooth out luck, and includes a comparison - a control group receiving no treatment or the standard treatment. When an answer choice says the groups differed in two ways, it is describing a broken experiment: any observed effect could come from either difference, so no conclusion is valid. Sample size matters too: one plant proves nothing, fifty plants prove plenty. The test loves scenarios with an obvious flaw - no control group, different starting ages, measurements taken on different days - and the correct answer always names the flaw in plain language. Practice by finding the flaw out loud each time; the pattern repeats.
Hypotheses, Predictions, and Conclusions
A hypothesis is a testable statement - if fertilizer A increases growth, then plants given A will be taller than controls after two weeks. It must be falsifiable: if no possible result could contradict it, it is not science, and answer choices often include one such trap (plants grow because they want to). The conclusion must stay inside the data: significant difference supports the hypothesis; no difference fails to support it, which is not the same as disproving everything. Correlation-only data cannot establish cause - two variables moving together always invites the answer that mentions other possible explanations. Read each conclusion choice and ask: does this claim more than the graph shows? If yes, cross it out.
Predicting Results
Prediction questions describe a change and ask what happens next. Run the causal chain: increase the independent variable, follow it through the mechanism, land on the dependent variable's direction - up, down, unchanged. Direction beats magnitude; the answer choices rarely need arithmetic, only the sign of the effect. When the mechanism is unfamiliar (some chemistry or physics context), the graph of prior data still reveals the pattern: find the trend, extend it one step. Two habits cover nearly every prediction question - identify what changes, then trace where its effect lands.
GED Science Experiments - Frequently Asked Questions
How many scientific reasoning questions are on the GED?
About nine of the 46 questions focus on experimental design and reasoning - roughly 20 percent. They span all content areas and require no memorized facts, only the rules above.
What is the difference between control and controlled variables?
Same idea: the conditions held constant across all groups so only the independent variable differs. Sometimes a separate control group is the comparison baseline - a group that receives no treatment.
Can a hypothesis be proven?
No - data supports or fails to support it. Answer choices claiming a hypothesis was proven true are almost always wrong; look for language that stays within what the data actually measured.
Experimental reasoning pairs with data reading - drill both from graphs and data on GED Science, then check the Science help page for the full blueprint. Short on time? A professional test taker can sit the entire exam for you - confidential, $299 flat, 98.6% pass rate.