GED and HiSET science — evidence and conclusions

A large part of the science test is not about science facts at all. It puts a small study in front of you — a gardener, a factory line, a ward, a news report — and asks what the result actually shows. That is the whole of this set: twelve studies described in words, one question each, and in every case the content is only the vehicle.

Three of them look alike at first and are deliberately different. A survey finds that people who drink more coffee report less stress, and both things were measured on the same day, which means the direction is unknowable: unhurried people may simply be the ones with time for a coffee. A study finds that students with tablets score higher, where the trouble is a third factor — whatever pays for the tablet tends to pay for other advantages too. A diet study reports five pounds lost without tracking exercise, where the trouble is a variable nobody watched. Reverse causation, a confounder, an uncontrolled variable: three separate faults that are usually taught as one slogan.

The rest covers the machinery. Which variable was changed and which was measured, on a conveyor belt whose speed is being altered. What must be held constant in a typing test run at two temperatures — with an option offering to hold the temperature constant, which would leave nothing to compare. Why a single patient who recovers proves nothing: not because one is a small number but because there is nothing to hold the case against. What a sample of a thousand fixes, and what it leaves exactly where it was. Whether measuring a plant's height answers a question about its yield. What four readings of one lightbulb — 800, 805, 795, 800 — say about the instrument rather than the bulb. Whether an engine that saves fuel at 40 mph and wastes it at 70 supports a claim of being twenty percent more efficient. And what a second experiment should do after a first one works: not repeat itself on the same people, but try a group that differs in the way that matters.

No tables, no charts and no images: every figure is written into its sentence, which is also how these questions can be read aloud or worked on paper.

Zestly is an independent study tool. It is not affiliated with GED Testing Service, which owns the GED test, or with the HiSET program, and it is not a test centre.

• Name the independent and dependent variables in a described investigation
• Say what must be held constant, and recognize the trap of holding the tested variable constant
• Explain why a single case supports no conclusion, and what a control group supplies
• State what a larger sample fixes and what it does not
• Tell reverse causation, a third factor and an uncontrolled variable apart
• Judge whether a measurement answers the question the study asked
• Read the spread of repeated readings as information about the instrument
• Decide whether a general claim survives its own data, and choose a next experiment that tests something new

Written for this exercise; every study is described in words, with no tables or charts. From the bank: "A researcher tests a new lightbulb by measuring its brightness in lumens. He records the following four readings: 800, 805, 795, and 800. What does the spread of these readings indicate?" The readings are tight, which says something about the measuring rather than about the bulb.