causal relationship
spurious relationship
independent variable :自变量一词来自数学。在数学中， 。在这一方程中自变量是x，因变量是y。将这个方程运用到心理学的研究中，自变量是指研究者主动操纵，而引起因变量发生变化的因素或条件，因此自变量被看作是因变量的原因。In mathematical modelling and statistical modelling, there are dependent and independent variables. The models investigate how the former depend on the latter. The dependent variables represent the output or outcome whose variation is being studied. The independent variables represent inputs or causes, i.e. potential reasons for variation. Models test or explain the effects that the independent variables have on the dependent variables. Sometimes, independent variables may be included for other reasons, such as for their potential confounding effect, without a wish to test their effect directly.
Effects of vitamin C on life span
In a study whether taking vitamin C pills daily make people live longer, researchers will dictate the vitamin C intake of a group of people over time. One part of the group will be given vitamin C pills daily. The other part of the group will be given a placebo pill. Nobody in the group knows which part they are in. The researchers will check the life span of the people in both groups. Here, the dependent variable is the life span and the independent variable is a binary variable for the use or non-use of vitamin C.
Effect of fertilizer on plant growth
In a study measuring the influence of different quantities of fertilizer on plant growth, the independent variable would be the amount of fertilizer used. The dependent variable would be the growth in height or mass of the plant. The controlled variables would be the type of plant, the type of fertilizer, the amount of sunlight the plant gets, the size of the pots, etc.
Effect of drug dosage on symptom severity
In a study of how different doses of a drug affect the severity of symptoms, a researcher could compare the frequency and intensity of symptoms when different doses are administered. Here the independent variable is the dose and the dependent variable is the frequency/intensity of symptoms.
Effect of temperature on pigmentation
In measuring the amount of color removed from beetroot samples at different temperatures, temperature is the independent variable and amount of pigment removed is the dependent variable.
Effect of education on wealth
In sociology, in measuring the effect of education on income or wealth, the dependent variable is level of income/wealth and the independent variable is the education level of the individual.
