How many questionnaires are collected when the data processing starts?

About 30%. Generally speaking, if the recovery rate is only about 30%, the data can only be used as a reference. Above 50%, suggestions can be adopted. When the recovery rate reaches 70%~75% or above, it can be used as the basis for research conclusions. Therefore, the recovery rate should generally not be less than 70%. If the response rate of valid questionnaires is less than 70%, another letter and a questionnaire will be sent for supplementary testing. In addition, in order to ensure the reliability of the conclusion, if possible, a small-scale follow-up survey can be conducted to understand the basic views of the subjects who did not answer the questions to prevent one-sided analysis of the questionnaire results. From the above conclusion, it can be seen that in educational survey research, if questionnaires are used, the response rate of valid questionnaires must be ≥70%. In other words, recovery rates lower than 70% cannot be used for research.