Source: U.S. Bureau of Justice Statistics, Criminal Victimization 1997, and previous bulletins.Criminal Victimization 1998, Changes 1997-98 with Trends 1993-98, series NCJ-176353 (revised 25 August 1999).

http://www.ojp.usdoj.gov/bjs/cvict.htm

*Survey methodology

The National Crime Victimization Survey (NCVS) collects data from residents living throughout the United States, includingpersons living in group quarters, such as dormitories, rooming houses, and religious group dwellings. Crew members ofmerchant vessels, Armed Forces personnel living in military barracks, and institutionalized persons, such as correctionalfacility inmates, were not included in the survey. Similarly, U.S. citizens residing abroad and foreign visitors to this countrywere excluded. With these exceptions, individuals age 12 and older living in units selected for the sample were eligible tobe interviewed.

Data collection

Each housing unit selected for the NCVS remains in the sample for 3 years, with each of seven interviews taking place at6-month intervals. An NCVS interviewer's first contact with a housing unit selected for the survey is in person. Theinterviewer may then conduct subsequent visits, except for the fifth, by telephone.

To elicit more accurate reporting of incidents, NCVS uses the self-respondent method which calls for the direct interviewingof each person 12 years and older in the household. An exception is made to use proxy interviewing instead of directinterviewing for the following three cases: 12- and 13-year-old persons when a knowledgeable household member insiststhey not be interviewed directly, incapacitated persons, and individuals absent from the household during the entirefield-interviewing period. In the case of temporarily absent household members and persons who are physically or mentallyincapable of granting interviews, interviewers may accept other household members as proxy respondents, and in certainsituations non-household members may provide information for incapacitated persons.

Approximately 30% of the interviews in the 1995 sample were conducted using Computer-Assisted Telephone Interviewing(CATI), a data collection mode that involves interviewing from centralized facilities and using a computerized instrument. Inthe CATI-eligible part of the sample, all interviews are done by telephone whenever possible, except for the first and fifthinterviews, which are still primarily conducted in person. The telephone interviews are conducted by the CATI facilities(Hagerstown, MD and Tucson, AZ).

Sample design and size

Survey estimates are derived from a stratified, multi-stage cluster sample. The primary sampling units (PSUs) composing thefirst stage of the sample were counties, groups of counties, or large metropolitan areas. Large PSUs were included in thesample automatically and are considered to be self-representing (SR) since all of them were selected. The remaining PSUs,called non-self-representing (NSR) because only a subset of them was selected, were combined into strata by groupingPSUs with similar geographic and demographic characteristics, as determined by the 1990 census.

The 1995 NCVS sample households were drawn from both the 1980- and 1990-based sample designs. The 1980 designconsists of 84 SR PSUs and 153 NSR strata, with one PSU per stratum selected with probability proportionate to populationsize. The 1990 design consists of 92 SR PSUs and 153 NSR strata, with one PSU per stratum selected with probabilityproportionate to population size. The NCVS sample design continued use of both the 1980- and 1990-based samples through1997. Beginning in 1998 only the 1990-based sample remains.

In the second stage of sampling, each selected stratification PSU is divided into four frames (unit, area, permit, and groupquarter) from which NCVS independently selects its sample. From each selected stratification PSU, clusters ofapproximately four housing units or housing unit equivalents are selected from each frame. For the unit and group quarterframes, addresses come from the 1990 census files. For the permit frame, addresses come from building permit dataobtained from building permit offices. For the area frame, sample blocks come from the 1990 census files. Then, addressesare listed and sampled in the field.

Approximately 58,520 housing units and other living quarters were designated for the sample. In order to conduct fieldinterviews, the sample is divided into six groups, or rotations, and each group of households is interviewed once every 6months over a period of 3 years. The initial interview is used to bound the interviews (bounding establishes a timeframe toavoid duplication of crimes on subsequent interviews), but is not used to compute the annual estimates. Each rotation groupis further divided into six panels. A different panel of households, corresponding to one sixth of each rotation group, isinterviewed each month during the 6-month period. Because the survey is continuous, newly constructed housing units areselected as described, and assigned to rotation groups and panels for subsequent incorporation into the sample. A newrotation group enters the sample every 6 months, replacing a group phased out after being in the sample for 3 years.

For these 58,520 sample households, complete interviews were obtained for approximately 47,750 households (95.1% ofeligible housing units). Within interviewed households approximately 89,900 persons (91.1%) provided responses. Of theremaining 10,770 housing units, 8,010 were determined to be ineligible (i.e., vacant, demolished, etc.), and the occupantscould not be reached or refused to participate in approximately 2,660 of the units.

Selection of cases for CATI

About 30% of the 47,750 households obtained in the 1995 sample were interviewed using the CATI technique. Currently,the NCVS sample PSUs fall into three groups of CATI usage: maximum-CATI PSUs, where all the segments in the PSU areCATI-eligible; half-CATI PSUs, where half of the segments in the PSU are randomly designated to be CATI-eligible; andno-CATI PSUs, where none of the segments are CATI-eligible. The level of CATI usage for each PSU was established withconcern toward an optimal workload for the field interviewers. In the "half-CATI" PSUs, a random sample of about 50% ofthe segments in each PSU is taken and designated as CATI-eligible. The sample cases in CATI-eligible segments from themax-CATI and the half-CATI PSUs are interviewed from CATI facilities while the other sample cases are interviewed bythe standard NCVS field procedures.

Accuracy of estimates

The accuracy of an estimate is a measure of its total error, that is, the sum of all the errors affecting the estimate: samplingerror as well as nonsampling error.

The sample used for the NCVS is one of a large number of possible samples of equal size that could have been obtained byusing the same sample design and selection procedures. Estimates derived from different samples would differ from oneanother due to sampling variability, or sampling error.

The standard error of a survey estimate is a measure of the variation among the estimates from all possible samples.Therefore, it is a measure of the precision (reliability) with which a particular estimate approximates the average result ofall possible samples. The estimate and its associated standard error may be used to construct a confidence interval. Aconfidence interval is a range of numbers which has a specified probability that the average of all possible samples, whichis the true unknown value of interest in an unbiased design, is contained within the interval. About 68% of the time, thesurvey estimate will differ from the true average by less than one standard error. Only 10% of the time will the difference bemore than 1.6 standard errors, and just 1 time in 100 will it be greater than 2.5 standard errors. A 95% confidence interval isthe estimate plus or minus twice the standard error. Thus there is a 95% chance that the result of a complete census wouldfall within the confidence interval.

In addition to sampling error, the estimates are subject to nonsampling error. While substantial care is taken in the NCVS toreduce the sources of nonsampling error throughout all the survey operations, by means of a quality assurance program,quality controls, operational controls, and error-correcting procedures, an unquantified amount of nonsampling errorremains.

Major sources of nonsampling error are related to the ability of the respondents to recall in detail the crimes that occurredduring the 6 months prior to the interview. Research based on interviews of victims obtained from police files indicates thatassault is recalled with the least accuracy of any crime measured by the NCVS. This may be related to the tendency ofvictims to not report crimes committed by offenders who are not strangers, especially if they are relatives. In addition,among certain groups, crimes that contain elements of assault could be a part of everyday life, and are therefore forgotten ornot considered important enough to mention to a survey interviewer. These recall problems may result in an understatementof the actual rate of assault.

However, as part of the 1992 redesign of the survey, substantial improvements were made to measure crime more accuratelyand, therefore, reduce the nonsampling error. The NCVS now includes improved questions and cues that aid victims inrecalling victimizations, more explicit questions are now asked about sexual victimizations, and new components have beenadded to measure victimizations by nonstrangers. As a result, victims are reporting more crime incidents.

Another source of nonsampling error is the inability of some respondents to recall the exact month a crime occurred, eventhough it was placed in the correct reference period. This error source is partially offset by interviewing monthly and usingthe estimation procedure described earlier. Telescoping is another problem in which incidents that occurred before thereference period are placed within the period. The effect of telescoping is minimized by using the bounding procedurepreviously described. The interviewer is provided with a summary of the incidents reported in the preceding interview and,if a similar incident is reported, it can be determined whether or not it is a new one by discussing it with the victim. Eventsthat occurred after the reference period are set aside for inclusion with the data from the following interview.

Other sources of nonsampling error can result from other types of response mistakes, including errors in reporting incidentsas crimes, misclassification of crimes, systematic data errors introduced by the interviewer, errors made in coding andprocessing the data. Quality control and editing procedures were used to minimize the number of errors made by therespondents and the interviewers.

Since field representatives conducting the interviews usually reside in the area in which they interview, the race andethnicity of the field representatives generally matches that of the local population. Special efforts are made to further matchfield representatives and the people they interview in areas where English is not commonly spoken. About 90% of all NCVSfield representatives are female.

Standard errors measure only those nonsampling errors arising from transient factors affecting individual responsescompletely at random (simple response variance); they do not reveal any systematic biases in the data. As calculated in theNCVS, the standard errors would partially measure nonsampling error arising from some of the above sources, such astransient memory errors, or accidental errors in recording or coding answers, for example. *Definitions of terms

Age--The appropriate age category is determined by the respondent's age on the last day of the month before the interview.

Aggravated assault--Attack or attempted attack with a weapon, regardless of whether an injury occurred, and attackwithout a weapon when serious injury results.

With injury--An attack without a weapon when serious injury results, or an attack with a weapon involving any injury.Serious injury includes broken bones, lost teeth, internal injuries, loss of consciousness, and any unspecified injuryrequiring 2 or more days of hospitalization.

Threatened with a weapon--Threat or attempted attack by an offender armed with a gun, knife, or other object used asa weapon, not resulting in victim injury.

Annual family income--The total income of the household head and all members of the household for the 12 monthspreceding the interview. Includes wages, salaries, net income from businesses or farms, pensions, interest, dividends, rent,and any other form of monetary income.

Assault--An unlawful physical attack or threat of attack. Assaults may be classified as aggravated or simple. Rape,attempted rape, and sexual assaults are excluded from this category, as well as robbery and attempted robbery. The severityof assaults ranges from minor threat to incidents which are nearly fatal.

Ethnicity--A classification based on Hispanic culture and origin, regardless of race.

Head of household--A classification that defines one and only one person in each housing unit as the head. Head ofhousehold implies that the person rents or owns (or is in the process of buying), the household unit. The head of householdmust be at least 18, unless all members of the household are under 18, or the head is married to someone 18 or older.

Hispanic--Persons who describe themselves as Mexican-American, Chicano, Mexican, Mexicano, Puerto Rican, Cuban,Central American, South American, or from some other Spanish culture or origin, regardless of race.

Household--A person or group of people meeting either of the following criteria: (1) people whose usual place of residenceis the same housing unit, even if they are temporarily absent; (2) people staying in a housing unit who have no usual place ofresidence elsewhere.

Household burglary--Unlawful or forcible entry or attempted entry of a residence. This crime usually, but not always,involves theft. The illegal entry may be by force, such as breaking a window or slashing a screen, or may be without forceby entering through an unlocked door or an open window. If the person entering has no legal right to be present in thestructure a burglary has occurred. The structure need not be the house itself for a burglary to take place; illegal entry of agarage, shed, or any other structure on the premises also constitutes household burglary. If breaking and entering occurs in ahotel or vacation residence, it is still classified as a burglary for the household whose member or members were stayingthere at the time the entry occurred.

Completed burglary--To successfully gain entry to a residence by a person who has no legal right to be present in thestructure, by use of force, or without force.

Forcible entry--A form of completed burglary in which force is used to gain entry to a residence. Some examplesinclude breaking a window or slashing a screen.

Unlawful entry without force--A form of completed burglary committed by someone having no legal right to be on thepremises, even though no force is used.

Attempted forcible entry--A form of burglary in which force is used in an attempt to gain entry.

Incident--A specific criminal act involving one or more victims and offenders. For example, if two people are robbed at thesame time and place, this is classified as two robbery victimizations but only one robbery incident.

Marital status--Every person is assigned to one of the following classifications: (1) married, which includes persons incommon-law unions and those who are currently living apart for reasons other than marital discord (employment, militaryservice, etc.); (2) separated or divorced, which includes married persons who are legally separated and those who are notliving together because of marital discord; (3) widowed; and (4) never married, which includes persons whose marriageshave been annulled and those who are living together and not in a common-law union.

Metropolitan Statistical Area (MSA)--Office of Management and Budget defines this as a population nucleus of 50,000 ormore, generally consisting of a city and its immediate suburbs, along with adjacent communities having a high degree ofeconomic and social integration with the nucleus. MSA's are designated by counties, the smallest geographic units for whicha wide range of statistical data can be obtained. However, in New England, MSA's are designated by cities and towns sincethese subcounty units are of great local significance and considerable data is available for them. Currently, an area isdefined as an MSA if it meets one of two standards: (1) a city has a population of at least 50,000; (2) the Census Bureaudefines an urbanized area of at least 50,000 people with a total metropolitan population of at least 100,000 (or 75,000 inNew England). The Census Bureau's definition of urbanized areas, data on commuting to work, and the strength of theeconomic and social ties between the surrounding counties and the central city determine which counties not containing amain city are included in an MSA. For New England, MSA's are determined by a core area and related cities and towns, notcounties. A metropolitan statistical area may contain more than one city of 50,000 and may cross State lines. Within thisgeneral classification unit, there are three subclassifications: urban, suburban, and rural. They are defined as follows:

Urban areas--The largest city or grouping of cities in a metropolitan statistical area.

Suburban areas--A county or group of counties containing a central city, plus any contiguous counties that are linkedsocially and economically to the central city. Suburban areas are categorized as those portions of metropolitan areassituated "outside central cities."

Rural areas--A place not located inside a metropolitan statistical area. This category includes a variety of localities,ranging from sparsely populated rural areas to cities with populations less than 50,000.

Motor vehicle--An automobile, truck, motorcycle, or any other motorized vehicle legally allowed on public roads andhighways.

Motor vehicle theft--Stealing or unauthorized taking of a motor vehicle, including attempted thefts.

Completed motor vehicle theft--The successful taking of a vehicle by an unauthorized person.

Attempted motor vehicle theft--The unsuccessful attempt by an unauthorized person to take a vehicle.

Non-Hispanic--Persons who report their culture or origin as something other than "Hispanic" as defined above. Thisdistinction is made regardless of race.

Nonstranger--A classification of a crime victim's relationship to the offender. An offender who is either related to, wellknown to, or casually acquainted with the victim is a nonstranger. For crimes with more than one offender, if any of theoffenders are nonstrangers, then the group of offenders as a whole is classified as nonstranger. This category only applies tocrimes that involve contact between the victim and the offender; the distinction is not made for crimes of theft since victimsof this offense rarely see the offenders.

Offender--The perpetrator of a crime; this term usually applies to crimes involving contact between the victim and theoffender.

Offense--A crime. When referring to personal crimes, the term can be used to refer to both victimizations and incidents.

Personal crimes--Rape, sexual assault, personal robbery, assault, purse snatching and pocket picking. Includes bothattempted and completed crimes.

Personal crimes of violence--Rape, sexual assault, personal robbery, or assault. Includes both attempted and completedcrimes; does not include purse snatching and pocket picking. Murder is not measured by the NCVS because of the inability toquestion the victim.

Completed violence--The sum of all completed rapes, sexual assaults, robberies, and assaults.

Attempted/threatened violence--The unsuccessful attempt of rape, sexual assault, personal robbery, or assault.Includes attempted attacks or sexual assaults by means of verbal threats.

Property crimes--Burglary, motor vehicle theft, or theft. Includes both attempted and completed crimes.

Purse snatching/pocket picking--Theft or attempted theft of property or cash directly from the victim by stealth, withoutforce or threat of force.

Race--Racial categories for this survey are white, black, and other. The category "other" is composed mainly of Asians,Pacific Islanders, American Indians, Aleuts, and Eskimos. The race of the head of household is used in determining the raceof the household for computing household crime demographics.

Rape--Forced sexual intercourse including both psychological coercion as well as physical force. Forced sexual intercoursemeans vaginal, anal, or oral penetration by the offender(s). This category also includes incidents involving penetration usinga foreign object such as a bottle. Includes attempted rapes, male as well as female victims, and both heterosexual andhomosexual rape. Attempted rape includes verbal threats of rape.

Rate of victimization--See "Victimization rate."

Robbery--Completed or attempted theft, directly from a person, of property or cash by force or threat of force, with orwithout a weapon, and with or without injury.

Completed/property taken--The successful taking of property from a person by force or threat or force, with orwithout a weapon, and with or without injury.

Completed with injury--The successful taking of property from a person, accompanied by an attack, either with orwithout a weapon, resulting in injury.

Completed without injury--The successful taking of property from a person by force or the threat of force, either withor without a weapon, but not resulting in injury.

Attempted to take property--The attempt to take property from a person by force or threat of force without success,with or without a weapon, and with or without injury.

Attempted without injury--The attempt to take property from a person by force or threat of force without success, withor without a weapon, but not resulting in injury.

Attempted with injury--The attempt to take property from a person without success, accompanied by an attack, eitherwith or without a weapon, resulting in injury.

Sexual assault--A wide range of victimizations, separate from rape or attempted rape. Includes attacks or attempted attacksgenerally involving unwanted sexual contact between victim and offender. Sexual assaults may or may not involve force andinclude such things as grabbing or fondling. Sexual assault also includes verbal threats.

Simple assault--Attack without a weapon resulting either in no injury, minor injury (for example, bruises, black eyes, cuts,scratches, or swelling), or in undetermined injury requiring less than 2 days of hospitalization. Also includes attemptedassault without a weapon.

With minor injury--An attack with or without a weapon resulting in minor injury (for example, bruises, black eyes,cuts, etc.) or in undetermined injury requiring less than 2 days of hospitalization.

Without injury--An attempted assault without a weapon not resulting in injury.

Stranger--A classification of the victim's relationship to the offender for crimes involving direct contact between the two.Incidents are classified as involving strangers if the victim identifies the offender as a stranger, did not see or recognize theoffender, or knew the offender only by sight. Crimes involving multiple offenders are classified as involving nonstrangers ifany of the offenders was a nonstranger. Since victims of theft without contact rarely see the offender, no distinction is madebetween strangers and nonstrangers for this crime.

Tenure--The NCVS recognizes two forms of household tenancy: (1) owned, which includes dwellings that are mortgaged,and (2) rented, which includes rent-free quarters belonging to a party other than the occupants, and situations where rentalpayments are in kind or in services.

Theft--Completed or attempted theft of property or cash without personal contact. Incidents involving theft of property fromwithin the sample household would classify as theft if the offender has a legal right to be in the house (such as a maid,delivery person, or guest). If the offender has no legal right to be in the house, the incident would classify as a burglary.

Completed--To successfully take without permission property or cash without personal contact between the victim andoffender.

Attempted--To unsuccessfully attempt to take property or cash without personal contact.

Victim--The recipient of a criminal act, usually used in relation to personal crimes, but also applicable to households.

Victimization--A crime as it affects one individual person or household. For personal crimes, the number of victimizationsis equal to the number of victims involved. The number of victimizations may be greater than the number of incidentsbecause more than one person may be victimized during an incident. Each crime against a household is assumed to involve asingle victim, the affected household.

Victimization rate--A measure of the occurrence of victimizations among a specified population group. For personalcrimes, this is based on the number of victimizations per 1,000 residents age 12 and older. For household crimes, thevictimization rates are calculated using the number of incidents per 1,000 households.

Victimize--To commit a crime against a person or household.

*