Data collecting and handling procedures

Data collecting and handling procedures

Data collecting within the LASA study takes place in different phases. These phases are described below.

1. Preparatory phase

We have used three data collection modes per participant: main face-to-face interviews, face-to-face medical interviews and self-administered questionnaires.

The main and medical interviews are computerized face-to-face interviews, consisting of different modules programmed with Blaise (since September 2011, before that we used INTERV). These modules consist of a series of questions about one or two topics. During the programming phase, multiple tests are performed to ensure that the program settings are correct. During face-to-face interviewing the responses of the interviewees are directly entered into a laptop computer by the interviewer.

The self-administered questionnaire is either a paper-and-pencil form or an online questionnaire, depending on the preference of the participant. Care is taken to achieve a format that is optimally readable and intuitive to fill out.

2. Data collecting

Interviewing of each wave starts in September with the main face-to-face interviews. Medical interview takes place a few weeks after the main interview. The full data collection cycle takes just over one year.

2.1 Main interview

Recruiting and training of interviewers

Interviewers are recruited from the three main geographic areas where the participants were recruited. They are selected on the basis of their affinity with older people, living in the neighborhood vicinity of our LASA participants, and knowing how to work with a computer.

Interviewers receive an interview guide and extensive training before they conduct their fieldwork. The training takes three or four days for first-time interviewers and one or two days for experienced interviewers. The interviewers are instructed about how to interact with participants (for example: what to do if participant is too busy to participate), get used to the laptop and the administration program, practice all the questions and tests, and do role-plays. The interviewers are also asked to perform a full test-interview with a person they know. During the last day of the training, the interviewers can share experiences with the whole group and discuss anything unclear to them. Finally, the interviewers receive further written instructions to read regularly and commit to memory. Fieldwork coordinators and support remain in contact with interviewers regularly by phone and organize formal get-togethers several time during data collection for evaluation and reflection.

Eligibility criteria for participants

Most participants who were interviewed during the previous wave of data collection and who are still alive will be contacted to participate in a new data collection wave. Two groups of participants are exempted: participants who during the last wave did not participate in the face-to-face interview but in a brief telephone interview instead, and participants who indicated that that they are not able to or do not want to participate anymore.

Contacting the participants

Interviewers indicate with how many participants they can make an appointment within the next few weeks. That number of participants living in the vicinity of the interviewer obtain an invitation letter and a leaflet. The invitation letter indicates that an interviewer will contact the participant to make an appointment for an interview of about two hours. The name and telephone number of the interviewer are stated in this letter and interviewers contact participants by phone within two weeks to schedule an appointment. Interviewers usually visit the participants at home. Participants who are not able to sustain a complete interview may be invited to participate in a brief telephone interview so that a minimum of data is still obtained from them.


When a participant is currently not able to or refuses to make an appointment, there are three follow-up possibilities: the interviewer and participant agree that the participant is contacted another time within a few months; the participant is contacted by another interviewer, who is trained to do a telephone interview instead of a complete interview; or the participant will not be contacted anymore by LASA. Also, during an on-going interview, the interviewer may offer a shortened version, which takes about one hour, or to interview the participant on two separate days, in case the full interview takes too long for the participant to sustain.

Audio-recording of interviews

All interviews are audio-recorded (if the participants consent), for two reasons. First, the fieldwork team and the researchers listen to randomly selected tapes to give feedback to the interviewers about the quality of their interviewing. Second, during the cleaning phase of the raw data, the audiotapes can be listened when data seem inconsistent or incomplete.


Participants are asked to provide informed consent, by signing an informed consent form. Participants are asked to give permission to LASA to contact their doctors in attendance for additional information.

The last part of the main interview

After the main face-to-face interview is completed, the interviewer verifies if the participant is also willing to fill out the self-administered questionnaire, and take part in the medical interview. Once a week the interviewer sends the data and reporting forms to the LASA fieldwork coordination office.

2.2 Medical face-to-face interview


About two months before the start of the medical interview, interviewers are recruited specifically for the medical interview. Medical interviewers have to have experience with physical contact with older people. Therefore, medical interviewers have to have an appropriate professional background, such as in nursing, medical assistant or physiotherapy. They also need to have affinity with older people and live in the vicinity of our participants. They also receive extensive training and instructions.

Contacting the participants

The medical interviewers contact those participants who agreed to participate with the medical face-to-face interview (or who are still in doubt) within three weeks after the main interview. The main interviewer leave information about the medical interview with the participant, including the name of the medical interviewer who will contact the participant. This information also includes some topics of the medical interview and the request to have the containers of their medications ready for inspection.

All medical interviews are audio-recorded as well. This interview takes about one hour and a half.

Psychiatric diagnostic interviews

One of the questionnaires that is being administered during the main interview is the CES-D, a screening questionnaire for depression. If the participant’s sum score (calculated by the interview programme) lies above a specific cut-off score, the interviewer notes this on the reporting form for the medical interviewer, who will ask the participant to take part in an additional psychiatric diagnostic interview following the medical interview (diagnosis of depression (DIS) and/or anxiety (CIDI) disorder).

2.3 Self-administered questionnaire

Self-administered questionnaires (usually about 24 pages) are left behind by the main interviewer. The medical interviewer who visits the participant a few weeks later collects the filled-out questionnaires. Participants can also send the self-administered questionnaire to LASA in a postage paid envelope. In case any pages are not filled out, these pages are send back to the participant to be completed. New questionnaires and reminders are sent after a period of about six weeks. Since 2015 participants can choose whether they want to complete a paper or a digital version of the questionnaire.

2.4 Telephone interview

There are two different telephone interviews to potentially replace the main interview. The first is constructed for participants who are not able to participate in the main interview anymore, and for participants who refuse to participate in the main interview. This interview takes about fifteen minutes, so substantially shorter and less burdensome. After a telephone interview, no invitations to take part in the medical interview and to fill in the self-administered questionnaire are made. The second type is to conduct a telephone interview with a family member or a caregiver when a participant is completely unable to participate (for mental or physical reasons). This proxy interview takes about ten minutes.

3. Data-entry: making raw data from written questionnaire

Data typists are recruited to enter written data from the paper and pencil questionnaires of the telephone interview and the self-administered questionnaire in raw data files. Typists are instructed orally and in writing. Data entry is done twice for all data. After comparing the two raw data files, any inconsistencies are resolved by checking the original questionnaires. After correction, raw SPSS data files are constructed. As such, the number of entry errors in the resulting raw data files is negligible. 

4. Data processing: transforming raw data into SPSS data files

Initially the data that are obtained during the computerized interviews are stored within the interview program Blaise on the laptops of the interviewers. For each module per participant a unique datafile is made. After receiving the interview data from the interviewers, the LASA datamanager processes the interview data through a series of preconstructed algorithms and transforms all unique interview data files into accessible raw SPSS data files. These resulting raw data files consist of data from all participants per unique module.

5. Constructing usable datasets

5.1 Data cleaning

The next step in the processing of the data is to clean the raw data by reviewing the remarks that were made by the interviewers on participant report forms. Also, alphanumerical data gathered during the interviews are coded. Complex problems such as inconsistencies in the data are resolved by obtaining the advice from LASA researchers. All cleaning steps are recorded in SPSS scripts: a data cleaning file.

5.2 Cleaning scripts

Running the SPSS cleaning scripts transforms the raw data files into cleaned SPSS data files. These scripts consist of statements labelling variables and values, the cleaning scripts, and scripts attributing (user defined) missing values. The names of variables and files are chosen such that to facilitate working with the data longitudinally. Specifically, the name of a variable is the same across measurement waves, but is preceded by a different letter indicating each wave.

5.3 Data checks

Resulting data are then checked for internal consistency and validity. If possible the data are also checked for longitudinal consistency. Such checks occasionally lead to changes in existing data from previous waves.

The resulting SPSS data files consist of data on a specific topic for all participants per wave. A distinction in file names is made to indicate whether the data are from the main interview, the telephone interview, the medical interview or the self-administered questionnaire.

For an overview of the topics within LASA and the corresponding data files, see below.