Variables in an experiment

Light duration is deliberately changed so it is the independent variable. In exams identify the independent variable as the factor manipulated by the experimenter.

The measured germination percentage is the dependent variable because it may change with temperature. In exams choose the measured outcome as the dependent variable.

Throwing force is kept constant so it is a controlled variable. Keep other influential factors constant for a fair test.

Changing both temperature and sugar amount makes the cause of the effect unclear. In a fair test change only one independent variable at a time.

Pot size may affect plant growth so it can become a confounding variable. It should be kept the same in all groups.

Concentration can be measured by the number of correct answers in a fixed time. A dependent variable should be clearly measurable.

Enzyme concentration also affects activity rate so it should have been kept constant. Conclusions weaken when another influential variable changes.

The changed distance is the independent variable and (2,\text{cm}) to (10,\text{cm}) is its range. A suitable range helps reveal a trend.

Bubble count is a proxy measure of the rate of photosynthesis. A proxy measure should be recorded consistently.

Changing both exercise type and duration makes it unclear which factor changed pulse rate. Only one independent variable should be varied.

The number of shakes can affect foam height so it should be controlled. A consistent procedure allows a fair comparison.

When initial masses differ percentage change gives a fairer comparison. It can be calculated using ( \frac{\text{final mass}-\text{initial mass}}{\text{initial mass}}\times100 ).

Temperature is not manipulated but measured to check constancy so it is a monitored controlled variable. Recording controls provides evidence of a fair test.

Too few closely spaced values may not reveal the trend clearly. Choose suitable intervals and an adequate range for the independent variable.

Plant species is usually a controlled variable because it is kept the same across groups. Merely being observed at the end does not make it dependent.

The number of batteries is deliberately changed and brightness is recorded as the outcome. The manipulated factor is independent and the measured outcome is dependent.

Surface area affects reaction rate so it should be kept constant. Acid concentration should remain the only independent variable.

Different instruments may change measurement precision so the measurement method should be kept consistent. Equipment can be part of the controlled conditions.

The starting point can affect travel distance and speed so changing it makes the test unfair. It should be the same in every trial.

Water amount can affect growth so it should be identical for all groups. This keeps soil type as the only manipulated factor.

Wire length is changed and resistance is measured. Material and thickness should be controlled.

Pressure depends on both depth and density so changing both creates confusion. Liquid density should be kept constant.

Mass loss in a fixed time measures the evaporation rate. Keeping the time interval constant makes the comparison fair.

Random order can reduce time-related effects such as equipment warming or gradual environmental change. This improves experimental validity.

Sleep duration is the independent variable so another influential factor such as age should be controlled. Age becomes independent when it is deliberately varied.