Question

what does researcher looks for when manipulating a variable?

Answer 1

A manipulated variable is an independent variable that can be changed in order to examine the cause and effect relationship between the dependent variable and the independent variable

for example in order to check whether, the amount of crop yield depends upon the amount of fertilizer applied then we can take the manipulated variable as amount of fertilizer and based on it perform the field experiments to measure the amount of yield and then perform the correlation and regression techniques to find the nature of relationship or we can be able to measure the linear relationship between the two by regression analysis.

a set of manipulated variables helps to reach at the conclusion which can be further applied in other statistical analysis like forecasting etc

in second case the manipulated variables can be applied in hypothesis testing for example we can check the effect of a drug on the certain number of patients, here the outcomes of the results of drug on number of patients is manipulated variables and we can check the significant effect of drug by applying a statistical test like t test etc