Understanding Society User Support

Many thanks for your enquiry. The Understanding Society team is looking into it and we will get back to you as soon as we can.

Best wishes,
Stephanie Auty - Understanding Society User Support Officer

Not really. The chance to be assigned to a particular monthly sample can be considered random, but within each monthly sample people interviewed early in the month (easy-to-contact and co-operative) are systematically different from those interviewed later. So, you'd probably be safe to compare, say, the Jan-Apr samples with the July-Dec samples. But for the May and June samples you would need additional controls for selection into before/after.

Follow-up question from Jing (by email):

You mentioned both May and June samples would not be random. I understand the June sample would be problematic, but I'm puzzled why the May sample should also be excluded. What makes the May sample different from, say, the April sample, since respondents were all interviewed before June, in which the Referendum took place?

Answer from me:

May sample members are not all interviewed in May. A non-negligible minority were interviewed after referendum day:

. ta g_istrtdatm if g_month==17

Interview |
  start date |
     (month) |      Freq.     Percent        Cum.
-------------+-----------------------------------
           5 |        786       53.76       53.76
           6 |        443       30.30       84.06
           7 |        140        9.58       93.64
           8 |         45        3.08       96.72
           9 |         23        1.57       98.29
          10 |         25        1.71      100.00
-------------+-----------------------------------
       Total |      1,462      100.00

. ta h_istrtdatm if h_month==5

Interview |
  start date |
     (month) |      Freq.     Percent        Cum.
-------------+-----------------------------------
     missing |          1        0.05        0.05
           5 |        635       32.95       33.00
           6 |        907       47.07       80.07
           7 |        246       12.77       92.84
           8 |         67        3.48       96.32
           9 |         48        2.49       98.81
          10 |         23        1.19      100.00
-------------+-----------------------------------
       Total |      1,927      100.00

Dear Jing Shen,

To answer your first question, no, the sampling strata and psu do not have any influence on the date on which an individual would be interviewed.

Regarding “easy-to-contact and cooperative households/individuals would be interviewed first, and difficult cases were dealt with later” – this isn’t a pre-determined state, that is, interviewers don’t deal with ‘easy’ cases first and leave the ‘difficult’ cases until later, they try to contact all the sample at around the same time, and those who are easier to contact are more likely to be contacted early. Those who are more difficut to contact are more likely to have missed interviews in previous waves as they may miss appointments, be difficult to get hold of, or reluctant. It takes interviewers more time to chase and interview these participants.

There is a large literature that looks at who are the easy-to-contact and difficult respondents, and this is also something that you could explore empirically with the data.

Best wishes,
Stephanie