I think that accuracy and integrity of responses is more possible in interviews than questionnaire methods - as clarifications and more extended replies can be got when required.

For getting accurate answer from questionnaire, we should frame it in such a way that question and its options should be more comprehensible. Questionnaires should take appropriate time to be responded. If a questionnaire is planned to be responded in 15 minutes maximally, it is better. The surveyor should not ask about such data which is time taking to obtain from records by respondents. If you question about the institution, it is better to take permission from the head of the concerned institute.

However, these are methods to get more reliable data. 100% accuracy and integrity is not possible in my view.

Prabhat Ranjan thank you. i hold your view too. but do you lengthiness of questions and the total required for filling the questionnaire affects integrity?

If it takes too long respondent might  become bored, not reading the questions properly and answering honestly

So a short and concise questions will be better than an elaborate and detailed question (usually for better understanding of the respondents)? 

I agree with Prabhat  Rajan that interview method should give more accurate data however, if questionnaire should be used, then the researcher should first consult a statistician, conduct a reliability test on the questions and above all must be knowledgeable in the field of study to guarantee integrity and accuracy of the data generated.

When one of the aims in study is seeking truthfulness, there are several things to consider, starting with your topic, and the type of information you are seeking. These are important factors in utilizing a qualitative survey design or qualitative interview, and the way the questions are worded to elicit truthfulness.

 If what you are after is an in-depth understanding of a topic, interviews provide the researcher an opportunity to interject clarification questions in between interview questions to make sure the researcher understands exactly what participants mean. This allows for a two-way interaction, which is sometimes necessary to gain a full perspective or clarify. If you do not think you will need this opportunity, a cloak of anonymity accompanies the process of collecting survey data, where participants remain anonymous, making some people feel more comfortable. However, because of this, some respondents may choose to give short, succinct, and careless responses. You may be able to avoid this if you design your study so that you meet respondents in person and give them the survey to fill out in the privacy of their home and return to you, giving you the opportunity to interject verbal instructions specifying to please be truthful in your responses.

 You can always design a study utilizing both approaches, giving participants the choice of completing survey questions or being interviewed…. Or…. hold an in depth interview initially, and do a follow up survey with questions to clarify information gained from the interviews….best of luck.