This document presents the survey and sample population, the results of the fieldwork, the representativeness of the sample, profile of cellphone owners, and research tool of the 2016 survey.
1.1 Survey and sample population
The target population consisted of Israelis aged 22+ at the time of the survey.
Sampling was conducted by an external sampling company (Data-Media), of two independent groups:
1. The computerized lists of landline consumers of Bezeq and HOT;
2. Lists of registered cellphone users who do not have a landline 1.
This system enabled us to improve the representativeness of the survey to include population groups that tend to have at least one landline or only a cellphone.
To ensure the representativeness of all population groups in Israel, we used stratified-hierarchical, sampling based on origin: Arabs or Jews, by ownership of a telephone: least one landline or only a cellphone.
1 This year, we developed a sampling system together with ICDC of residents who have only cellphones. According to the data on the distributions of populations with only cellphones, about 50% are in the 21-34 age group and 25% – in the 35-44 age group. Furthermore, the Arab population showed a higher rate of people who have only a cellphone (40%) than did the general population. This sampling system better represents these groups than that of the previous rounds of surveys.
The gross size of the sample was set to adequately represent each category. Note that sampling was random without identifying the respondents by their health plan, state of health, or use of health services; these data were collected by a questionnaire. The sampling company worked according to the abovementioned stratified-hierarchy. We obtained all the telephone numbers of every individual sampled, whether landline or cellular.
1.2 Results of fieldwork
The 2016 survey, like that of 2014, showed a very high response rate – 68%. In recent years, the percentage of readiness to respond to the request of interviewers (in surveys in general) has declined worldwide. Yet, compared with most surveys conducted today, the Myers-JDC-Brookdale Institute has managed to maintain a high response rate.
In this survey, in accordance with the request of the Ministry of Health (MoH), we hoped to reach a larger net number of interviewees than in the previous one; we interviewed 2,513 people vs. 1,540 in 2014. This high number enabled us to examine in depth the experience of subgroups that exhibit greater or more frequent use of health services, and to compare the findings with the findings for the general population. It also enabled us to achieve adequate representativeness of insurees from the small health plans and the Arab population.
Tables 1 and 2 summarize the findings of the fieldwork in the 2016 survey.
1 Omitted from the sample: People aged 22-, businesses and institutions, foreign residents, fax and modem numbers. Also omitted were telephone numbers of non-working lines or for which there had been no response for two months.
The profile of those who had only a cellphone and the correlation between landline ownership and the study variables is summarized in section 1.4 below.
1.3 Examination of representativeness of sample of respondents aged 22+ (according to data of the National Insurance Institute [NII])
We examined how representative the sample was by the variables of age, sex, health plan, district, Arabs/Jews.
This is the distribution of interviewees vs. the population aged 22+. These data are not weighted for the general population. The examinations of representativeness showed virtually complete correspondence between the distribution of the general population and of the sample population on the variables of health plan, sex, district, and national affiliation.
1. Health plans
The distribution into districts followed the definitions of the Central Bureau of Statistics (CBS). The following tables show population distributions by district for ages 22+, based on special processing by the National Insurance Institute (NII).
This is the distribution of Health Plan Membership, by district, for the general population vs. the sample.
As may be seen from the three tables, the 45+ age group is overrepresented and the 22-44 age group is underrepresented in the sample. Young people who have hardly any contact with the health system tend not to respond to these types of surveys. Nonetheless, the sample does resemble the age distribution of health-plan members vs. that of the general population.
Because of the difference in age distribution between the sample and the population, we took two steps: (a) We presented the central variables that showed significant differences by age in the theoretical statistics of age divisions. Also, in all the multivariate models, age was one of the controlling variables. (b) We weighted the entire sample by age; i.e., the results presented are adjusted for age.
5. National Affiliation
The calculations for the data of national affiliation of the 22+ age group were based on the statistical yearbook. There is no way to calculate the distribution of health-plan membership by national affiliation using CBS or NII data.
1.4 Characteristics of people who have only a cellphone vs. people with at least one landline
As said, this year, to expand the representativeness of the sample among people who have only a cellphone, we developed a sampling system together with ICDC to interview them as well.
The objective of this chapter is to examine whether the addition of people with a cellphone to the study population can impact the comparison with previous years.
The examination was conducted in two stages: In the first, we looked at the profile of people with only a cellphone vs. people with a landline; in the second, we looked at the main variables that had been examined over time, by telephone ownership.
Stage 1: Profile of cellphone owners
According to the national data collected by ICDC, some 50% of the people who had only cellphones were in the 21-34 age group, and 25% were in the 35-44 age group. Among Arabs, the rate of people who had only cellphones was higher (40%) than among the general population.
Like the national data, the survey of interviewees also showed a high rate of young people who had only a cellphone, as much as 57%. Note however (as above) that the rate of young interviewees was lower than the distribution of young people in the population. The young make up 50% of people with a cellphone only vs. 28% of the interviewees.
Again, like the national data on cellphone owners, the rate of Arabs with only a cellphone was higher than the rate of Arabs owning a landline. Arabs constitute 37% of people with a cellphone only vs. 17% of the interviewees.
Consistent with the tables, a logistic regression multivariate analysis of people who had only cellphones showed a likelier profile for young people, Arabs and Jerusalem residents. No differences were found by sex or health plan.
Stage 2: Distribution of Main Variables, by Telephone Ownership
A number of measures that we have been following over time were examined by landline ownership to verify the congruence of the comparison with previous years. For most of these variables, we found no significant differences by telephone ownership. The research report will specify differences by landline ownership for every variable. The examination revealed that even though people who had only a cellphone were added to the study population, it is possible to compare the surveys over the years.
1.5 Research Tools and Data Collection
The data were collected in telephone interviews, lasting some 20 minutes on average. They were conducted in Hebrew, Arabic, and Russian to facilitate appropriate representation of the population.