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Glossary and Acronym List Glossary Around the Airport Airfield The maneuvering area for aircraft, including the gates, apron, taxiways, and runways. Also referred to as airside. Airport user For the purpose of this guidebook, an airport user is anyone using the facilities on the airport property, whether as an air passenger, greeter, or well-wisher; an employee; or someone picking up or delivering cargo, doing business at the airport, making deliveries to the airport, or just sightseeing. Airside See airfield. May include the area of the terminal beyond security. Arrivingdeparting Also known as A-D passengers, this refers to the number of air passengers passengers on the plane when it arrives or departs. A-D pas- sengers include passengers that remain on the plane during any stopover. Connecting passengers Air passengers that transfer between flights at the airport. These passengers are an important statistic for terminal activity. Curb area Also known as the curbside or curb front, it is the area imme- diately in front of the terminal where vehicles are permitted to drop off and pick up passengers. Enplaneddeplaned Also known as E-D passengers, this is the most commonly air passengers used statistic for air passengers and refers to the number of passengers that get on (enplane) or get off (deplane) each flight. It includes connecting passengers. There are more A-D passengers than E-D passengers. Groundside The portion of the airport property dedicated to vehicle usage, including the roadways, parking lots, and curb area immedi- ately adjacent to the terminal. Sometimes also referred to as landside. Landside See groundside. May include the area of the terminal before security. Load factor Ratio of passengers to passenger seats on a flight. 146

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Glossary and Acronym List 147 Origindestination Also known as O-D passengers, this is the number of passengers air passengers starting or finishing their air trip at the airport. It is an impor- tant statistic because it relates to the number of passengers that will use the groundside area and airport access roads. The difference between O-D and E-D passengers is the connect- ing passengers. Pay on foot machines Parking payment machines that are normally inside the ter- minal building and are provided for easy payment of parking fees before returning to the vehicle to exit the lot. This saves time at the exit booth from the parking lot. Planning peak day The amount of activity, passengers or vehicles that occurs during a single day. This is not the highest day of activity, but is representative of a typical day in the peak month. Planning peak hour The amount of activity, passengers or vehicles that occurs during a peak hour for planning purposes. Typically either the 85th highest hour of activity over a year, or the busiest hour of a typical day in the peak month, is used as the plan- ning peak hour. Planning peak period A period of the year that is considered the appropriate level of demand for future planning. This period is not the highest peak, but is representative of a typical day in the peak month. Terminal Usually refers to the main air passenger facility or facilities. Ticket spitter The machine at the entrance to the parking lot that dispenses the ticket showing the time and date of entry. Statistical Terms Bias The amount an estimate differs from a true population value because of some quality of the measurement device, sample selection method, or other aspect of the survey. Central Limit Theorem The Central Limit Theorem is a statement about the charac- teristics of the sampling distribution of means of random samples from a given population. That is, it describes the characteristics of the distribution of values we would obtain if we were able to draw an infinite number of random sam- ples of a given size from a given population and we calculated the mean of each sample. The Central Limit Theorem consists of three statements: [1] The mean of the sampling distribution of means is equal to the mean of the population from which the samples were drawn. [2] The variance of the sampling distribution of means is equal to the variance of the population from which the samples were drawn divided by the size of the samples. [3] If the original population is distributed normally (i.e., it is bell shaped), the sampling distribution of means will

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148 Guidebook for Conducting Airport User Surveys also be normal. If the original population is not normally distributed, the sampling distribution of means will increas- ingly approximate a normal distribution as sample size increases (i.e., when increasingly large samples are drawn). Cluster sampling A sample selection method where individuals in the popula- tion belong to natural groups, or clusters (e.g., passengers on airplanes), and members of the population are selected first by selecting a sample of clusters, then selecting all or some of the individuals within each selected cluster (the latter case is a two-stage sampling scheme--see multi-stage sampling). Confidence interval A range above and below the estimated value that may be expected to contain the true value with a known probability. The known probability is referred to as the level of confi- dence. For example, a 95% confidence interval implies that if 100 samples were taken, we would expect the confidence inter- val to contain the true population value in all but five cases. Dataset Data, which is usually stored electronically, collected in a par- ticular survey. Estimate The value of a measure of some characteristic of the popula- tion that is determined from the sample. Estimation The process of producing an estimate. Mean The average of the values of a particular characteristic of indi- viduals in the population. Median A measure that identifies the middle-point value (or 50th per- centile) in a set of values when they are arranged in order of magnitude. Thus 50% of the sample is greater than this value and 50% is smaller. Mode The most common value of a particular characteristic in a sample. Multi-stage sampling A sample that is selected in stages, where the sampling units at each stage are subsamples from the previous stage. Non-probability sampling A sampling selection method where it is not possible to deter- mine the probability of individuals being selected. Non-proportional A sampling method where different sampling fractions are stratified sampling used to improve the accuracy of estimates for a given overall sample size. Percentage points Refers to the numerical value of a variable which is expressed as a percentage. For example, a range of 50% 5 percentage points is equivalent to the range 45% to 55%. Population The target population is the entire group of individuals about which information is desired. The survey population is the group of individuals that have a chance of being selected for the sample. The survey population should ideally be identical to the target population, but may not be exactly the same in practice.

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Glossary and Acronym List 149 Probability sample A sample selected in such a way that each individual in the population has a non-zero chance of being included and, in principle, the probability can be calculated. Proportional stratified A sampling method where the proportions of individuals in sampling each group (referred to as the sampling fractions) are equal. Random sampling A probability sample selection method where each member of the population has an equal probability of selection. Sample A subset of the population that is chosen to be representative of the total population and that can therefore be used to make generalizations about the population. Sample mean The average of the values of a particular characteristic of indi- viduals in a sample. Sample size The number of individuals composing the sample. Sample variance Sample variance of a particular characteristic is a measure of the spread, or dispersion, of values of that characteristic within a set of sample data. Sampling fraction The ratio of the sample size to the population size. Sampling frame A list of all members of a population used as a basis for sampling. Sampling plan Also referred to as sample design or survey design, the sam- pling plan specifies the type of sampling to be used (e.g., single or multi-stage, random, sequential, stratified, cluster sam- pling), the definitions of strata or clusters, and the sample size. Sequential sampling Also known as systematic sampling. A probability sample selection method in which the sample is obtained by select- ing every nth individual in the population, where n is an inte- ger greater than 1. The first member of the sample must be selected randomly within the first n units. Standard deviation A measure of the spread or dispersion of a set of data. It is calculated by taking the square root of the variance. The more widely the values are spread out, the larger the standard deviation. Standard error of the A measure of the amount of sampling error present. The estimate (SEE) standard error is an estimate of the standard deviation of the sample mean, based on the sample data. Stratified sampling A probability sample selection method in which the population is divided into homogeneous groups (strata) and members of each strata are sampled, possibly using different sampling methods. Systematic sampling See sequential sampling. Variance A measure of the spread or dispersion of a set of data. It is cal- culated by summing the square of the difference between each value and the mean value of the data.

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150 Guidebook for Conducting Airport User Surveys Surveying Terms Categorical question A type of closed-ended question that allows respondents to select one or more predefined responses. Census Survey of the total population of interest. Closed-ended question A type of survey question that has a finite set of answers pre- determined by the researcher from which the respondent chooses. Easy to standardize and lends itself to statistical analysis. Coding The process of converting answers to questions into numer- ical form (codes) to facilitate compilation of survey statistics. Computer-aided personal The use of an electronic device programmed with a survey interviewing questionnaire, including interviewer instructions, to interview people in person. Interview types to which this technique applies include on-site intercepts and in-office interviews. Computer-assisted The use of a computer to support telephone interviews by telephone interviewing displaying questions and allowing the interviewer to enter responses. Electronic data collection An electronic unit, such as a personal digital assistant, that device can be programmed to display survey questions and allow responses to those questions to be entered and stored in the unit. See computer-aided personal interviewing. Intercept interview A type of interview survey where respondents are approached (or intercepted) in high-traffic locations. Internet survey See Web-based survey. Interviewer A person who collects information from individuals in the sample by conversing with the individual. Interviewer bias A type of non-sampling error caused by the interviewer. Errors may include influencing the respondent in some way, asking questions in the wrong order, or using different phrasing or tone of voice than other interviewers, as well as intentional errors such as fraudulent data entry. Mail survey A survey methodology in which the questionnaire is distrib- uted to the target sample by mail. Multiple-choice question A type of closed-ended question that allows respondents to select the most appropriate answer from among a set of pos- sible answers. Good for "profiling" respondents. Mystery shopper survey A type of survey that anonymously evaluates customer ser- vice, operations, employee integrity, merchandising, and product quality of concessions and service providers. Non-representative sample This type of sample occurs when the characteristics of respondents in a survey do not match those of the desired target population.

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Glossary and Acronym List 151 Numerical question A type of closed-ended question that allows respondents to give a numerical value. Example: What is your current age? Open-ended question A type of survey question to which there are no predefined responses. Allows respondents to answer in their own words. Used in exploratory research. Pilot survey A small trial run, or "dress rehearsal," of the entire survey process completed before the actual survey commences. The intention is to alert the survey team to any difficulties that were not anticipated at the survey planning stage. Pilot sur- veys are conducted after pre-tests. Pre-test A small trial run of questions or the questionnaire to be used in the survey. The intention is to alert the survey team to problems with the questions such as confusing wording, inappropriate responses, additional responses to closed-ended questions, incorrect flow of questions, inappropriate length or format of questionnaire, etc. Respondent A person who is providing responses to a survey. Response bias Difference in the mean of the characteristics of interest between survey respondents and the population being surveyed. Sample bias This type of bias may result if the sample is limited only to respondents within a certain demographic group (e.g., highly educated). If the survey goal is to measure the opinions of the general population, this could bias the sample. Self-completed survey A survey in which respondents complete the questionnaire themselves. Survey codebook A document prepared by the survey planning team to code responses to questions in the survey. This document could be used as an aid in the data entry process or incorporated in the data entry software. Survey implementation team Team responsible for conducting the field work, performing data entry, and validating and cleaning the data. Survey method Method used to collect the survey data (e.g., intercept or tele- phone interviews or self-completed questionnaires handed out or distributed via mail or email). Survey planning team Team of people responsible for the design, conduct, and reporting of results. Includes the project manager, survey technical expert, survey sample design expert, data analyst, survey logistics manager, and survey administrator. Surveyor Person who collects information from or about individuals in the sample by observation or by interview. Telephone survey A survey methodology in which respondents are interviewed by telephone. Advantages include broad reach to potential respondents, and interviewers can ask clarifying questions.

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152 Guidebook for Conducting Airport User Surveys Web-based survey A survey methodology in which respondents complete a ques- tionnaire online. Advantages include rapid response rate, low cost, and increased respondent flexibility. Also called an Internet survey. Other Useful Glossaries Super Survey: Organization for Economic Cooperation and Development Glossary of Statistical Terms: European Society for Opinion and Marketing Research Glossary: php/glossary-a.html Acronyms and Short Forms AVI Automatic vehicle identification CATI Computer-assisted telephone interviewing EDCD Electronic data collection devices FAA Federal Aviation Administration MPO Metropolitan planning organization OAG Official Airline Guide PDA Personal digital assistant RFP Request for Proposals SAS Statistical Analysis Software, copyright of SAS Institute, Cary, NC SEE Standard Error of the Estimate SPSS A statistical software program, copyright of SPSS Inc., Chicago, IL TSA Transportation Security Administration