Respondent selection, as I mentioned before, this is a kind of extra step in the sampling process that comes about often when the units in the sampling frame don't match the units of analysis that the study is oriented towards. So that if for example, the frame lists households say, street addresses or landline telephone numbers, but the survey is about Individuals, as is often the case. Then this extra layer of sampling is necessary within the household to pick just one member to be the respondent from among all the household members. There are a number of different techniques for doing that. We won't go into all of them. Just to touch on a few of the well known ones, and a hybrid one, the best known is the Kish method, which is generally considered the gold standard. It's actually the oldest. It produces by far the most random sample and assures equal probability of selection. It's also considered to be the most intrusive because it requires respondents or household members to reveal considerable information about the household. The birthday methods are much simpler. They simply involve asking who in the household had the last birthday or the next birthday. They're much simpler, but they don't necessarily reveal the probability of selection. Because they don't require the number of people in the household to be indicated by the respondent. So there's a trade-off, but they are simpler to administer. And then the Rizzo, Brick, and Park model actually uses either the birthday method or Kish and makes use of just sort of coin toss techniques. So there are a number of other approaches to selecting a person within a household besides using one of these selection methods. There's, of course, no sampling, just interviewing the person who opens the door or answers the phone. And you can give some thought to why this might bias the sample. You're invited to post your thinking about this in one of the discussion boards. Or the interviewers might simply select the most knowledgeable respondent. So, this is somebody who can generally talk about the entire household or, and provide family level information. This is not necessarily somebody who's recruited at random. Quota methods are another technique that are used in which, for example, for some households the designated respondent is a female, and for others the designated respondent is a male. And then there are the probability or sometimes called quasi-probability methods that I've already alluded to, the Kish selection method and the birthday methods, and then there are others. So turning to the Kish method, just to give you a taste of it, it's a little more complicated than what we'll cover here. The interviewer asks the household member to list all of the people living in or who are members of the household or living in the housing unit and then indicate which of them is eligible to take part in the survey. So that might require that they be over 18 years of age, for example. It varies from study to study. So once there's a roster, it's called, of the eligible household members, then the interviewer asks the household member to number or order the eligible males from oldest to youngest and the eligible females from oldest to youngest. Then with these really two rosters in hand the interviewer uses what's called a selection table. And there are 8 selection tables that randomly allocate household members to be the respondent. So this is an example of what one of the selection tables might look like. Keep in mind that there are others that are randomly assigned to cases or households. So the selection table will indicate in a row the number of eligible persons in the household and then which of them will be selected as the respondent. So of course if there's just 1 eligible person in the household, that person, it's person number 1 is selected. That goes without saying. If there are 2, it could be person 1 or person 2. And in this selection table it's person 2. Another selection table would say in a 2 person household, it's person 1. If there are 3 people in the household, this selection table points to person 2, but another table would point to person 1 or person 3. And if there are 4 or more, this table selects person 3. Again, other tables would select other people. And so when these are all combined and equally distributed, every household member for every household size has an equal probability of selection. This is the great advantage of the Kish Method that it's the most precise election method and gives every household member an equal and known probability of selection. Disadvantages are that it requires gender and age of all eligible household members to be produced by the household member that the interviewer was speaking with. And that's time consuming and can be intrusive. This is that the interviewer's a stranger at this point to the household member. And so this may be a lot of information that feels personal to give to a stranger. And it may be subject to interviewer error just because it's complicated. And interviewers may make mistakes recording this either in a manual way more likely these days entering it into a computer. It can be automated and, for example, extended to over sample groups of particular interest, like teenagers or males, etc. So the Kish method is still in widespread use despite these drawbacks. It still has this one advantage that it's a very precise selection method. The birthday methods are last birthday, next birthday, example wording is, may I speak to the person of the household who is 18 years of age or older, and whose birthday was most recent? That would be the last birthday method. The next birthday method's exactly the same, except instead of was most recent would be is next. And so the interviewer asks to speak to the adult member of the household who has the next birthday. So advantages of the birthday methods, they're relatively easy to administer. They yield an equal probability of selection within a household. Anyone has the same chance of having had the most recent or the next birthday. They're much less intrusive than the Kish method, and they're brief. It's low effort for the household member in comparison to what happens when the Kish method is used. And it generates a sample that's more or less random. Disadvantages are that the exact chance of selection is unknown. So while there's an equal chance of selection, we don't know what the actual chance of selection is. And for this reason, this has been called a quasi-probability method. It's subject to reporting error because it becomes evident quickly why the interviewer is asking about birthdays. And so for a household member who doesn't want to be selected it's easy to indicate that somebody else had the most recent birthday. And it's difficult to verify that the report is truthful. And so it's for these reasons that Biemer and Lyberg recommend against using the birthday methods in what they call rigorous scientific studies. As I said there are a number of other methods. The paper by Gaziano goes through them and critiques them and nicely compares them. A comparison of the Kish Method and the birthday methods was conducted by Binson and her colleagues looking at dropouts in the two methods in a random digit dial telephone study. Overall the Kish method performed worse, that is led to more drop outs, and the next birthday method best, with last birthday method in between. You can see the dropout rates here. Kish is the highest, and next birthday is lowest. What was surprising was that much of this effect occurred before the respondent could know what type of screener questions they would be asked. In other words they really didn’t know what would follow. So you can see the percent who dropped out before the end of the introduction, that is before the interviewer had actually administered the screening process, was highest for Kish and last birthday, and lower for next birthday. So, it's as if the Interviewers are telegraphing to the respondents, to the household members what would follow. As if they were somehow indicating that the Kish method's going to be quite burdensome, and as a result, the household members terminated the interaction at that point. There's no guarantee this is exactly what happened. But I mean, the empirical result is that the Kish method did promote dropouts, and so in that sense, was less successful when it came to recruitment. And presumably this has something to do with its burden. Whether this was evident before the method was actually administered or not is not 100% clear. But it seems likely from this study. More recently a hybrid model has been proposed that is much less invasive than a Kish alone, and in most cases, can be explicit about the probability of selection. So there's a compromise here, but the idea is this is sort of the best compromise. And so the way it works is that the interviewer asks the respondent in a screener interview, that is before the actual interview begins, how many adults are in the household? If there's just one, if it's a one adult household, then that person, the screener respondent is selected, and that's the end of the selection process. If more than one adult was in the household, then a random selection process is administered. So that if there are two household members, and the screener respondent is not selected, that is the person providing answers to the questions like, how many people live in this household? If that person is not selected, then the other person is selected as sort of a coin toss. What this means is that there's no need to engage in a selection method like the Kish method. If there are more than two people and the screener respondent, the person the interviewer's talking to, is not selected, then and and only then, this eliminates a lot of situations. Only then is the last birthday method used. In very rare cases where birthdays are unknown, the Kish method is used. So it really reduces the number of situations, the number of cases, the number of occurrences of using any selection method, but particularly the Kish method. So this was tested, well developed, and tested by Rizzo et al., in a study of where Americans acquire their health information. As a kind of first check their work, the proportions of males and females who were selected were close to what is expected from the current population survey. So that's an indication that this is working well. As an indication that this really did reduce the amount of what they called additional sampling, that is using the birthday method or the Kish method, you can see that when there was 1 person, of course, no additional sampling is needed. Where there are 2 people, no additional sampling is needed. It's basically a coin toss. When there are 3 people, adults in the household, additional sampling is needed two-thirds of the time, that is when the screener respondent is not selected. And it continues like that. When there are 4 people, additional sampling is needed three-quarters of the time. When there are 5 or more, additional sampling is needed 85% of the time. But this substantially cuts down the number of households that need additional sampling when you look overall to 12.2%. So that's a great savings when you look at the impact of this procedure on break-offs or dropouts, for example. So choosing among the alternative selection methods, they're all subject to response error. So the Kish method requires the household member to enumerate who lives in, all members of the household. And that may not be entirely truthful. The birthday methods make it evident why the question is being asked in the first place. And this is something that a household member can manipulate if he or she doesn't want to participate. Full listings of household require that the interviewer explain the rationale to the respondent, or to the household member who's being asked to provide this information. And that may affect response rate in some cases. As we saw there was more dropout in Kish than in birthday method which doesn't require a full enumeration. Finally there are different organizational cultures regarding preferences for the different methods. So some survey shops just use one of these or predominantly use one of these. And then different clients have different preferences. So a survey organization will change the selection method depending on what the client believes to be the most appropriate. We'll talk next about a related topic known as proxy responding. And the issue there is what if the respondent, the household member who has been selected as a respondent isn't available? Is it acceptable to have another household member, usually the household member who is engaging in the selection process serve as a proxy, a surrogate, for the household member who has been selected? This differs from survey to survey, organization to organization. But it is done, and it can save costs by making it unnecessary for an additional phone call or an additional visit to a household to be made if the interview can be conducted then and there. So we'll turn to proxy responding next and take a look at what the implications are for response quality.
