Critical Value is the value that a test result must exceed in order for the researcher to conclude that the treatment or intervention he applied has a significant effect on the variable being investigated. It is the cut-off that will determine whether a test result represents a real difference, or if it is something that could have just occurred by chance.
When a researcher conducts a study, the data that he gathers needs to be converted into an appropriate statistic, in order for them to be analyzed and interpreted. For example, if he was using a statistic called the t-test, he would convert the results into a t-value. This t-value will then be compared to a critical value, that is determined by referring to a table that lists down critical values for the t-test. Any value higher than the critical value will cause the researcher to conclude that the treatment he applied has a significant effect on the variable under study.