CRIM 430

Sampling & Data Collection

Simple Random

List of elements in sampling frameNumber each elementSelect a number from the random numbers table arbitrarilyThe number selected indicates which element should be selected firstMove in constant direction on the random number tables until all sample spots are filled

Simple Random Example

Sampling Frame Random Numbers

1. Frank Blue 01209

2. Dana Boots 30254

3. David Heinz 52459

4. Jane Dear If you wanted a sample of 3, who would you pick given the random numbers above?

5. John Doe

6. John Smith

7. Sara White

Systematic Sampling

List of elements from sampling framePut in order (alphabetical, chronological, etc.)Calculate the nth element for selection by dividing the number desired by the total number in the sampling frameStart a random point and go down the list, selecting every nth element until you’ve reached your sample size

Stratified SamplingModification to previous methodsEnsures a degree of representativenessFirst, population is organized into homogeneous subsets (all males, all females)Sample elements are selected using the simple random or systematic methodOnce appropriate sizes for each group is me, the sample elements are placed back together to create the whole sample.Sample distributions of stratified variable equals the population distribution

Disproportionate StratifiedUsed when members of a population vary widely in size (e.g., 90% Male & 10% White)—it ensures that you receive an appropriate number of “rare” casesSame methods as stratified sampling except the distribution of the stratified variable is greater in the sample than it is in the population (I.e., the sample may=50/50 males and females)The “rare” cases are over-sampledTo compensate for this, data can be weighted during analysis to reflect population distributions

Multi-Stage Cluster Sampling

Used when there are many “layers” to the target population (e.g., police officers from all metropolitan departments across the United States)First, apply sampling to select departmentsNext, apply sampling to select police officersSampling is done in stages or clustersMore clustering results in potentially less representativeness

Non-Probability Sampling

Probability sampling designs are not possible in many situationsNon-probability sampling is an alternative; however, the samples are not representative of the population from which they are drawnNon-probability sampling designs are prone to selection biasNon-Probability sampling designs are, therefore, weaker than probability sampling designs

Non-Probability Sampling Designs

Purposive or Judgmental Sampling: Identifying a sample based on the presence of a particular characteristicQuota Sampling: Identifying a sample using a matrix to represent the characteristics of the populationConvenience Sampling: Sample is selected because access is easy and convenientSnowball Sampling: Using one respondent to provide contact to 2-3 additional respondents—continuous process to identify a larger sample

Types of Data CollectionSelf-Report Data

Data derived from the respondent him/herself Key=Ask questions to subjects Example: National Crime Victimization Survey

Official Data Data derived from agency records or databases Key=Examine written records Example: Uniform Crime Reports

Observation Data Data derived from watching the activities of people or

events; information is coded by observer Key=Watching behavior Example: Coding the behavior of detention officers and

offenders at a correctional institution

Data Collection: Asking Questions

Asking questions provides an indirect measure or substitute for making observations—Used to capture things such as experiences with crime, attitudes and beliefsSelf-administered surveysMailed surveysIn-person structured interviewsTelephone interviewsFocus groups

Asking Questions, Cont’d.

Types of questions included in surveys Open-ended Close-ended Statements with levels of agreement Contingency questions (if yes, proceed; if no, skip

to)

Presentation of questions in a survey Should be clear—avoid ambiguity & confusion Keep items short and to the point Keep items neutral and unbiased Add disclaimers/introductions to provide

respondent with direction

Assessment

Strengths Useful in describing large populations Standardized surveys improve strength of

measurement Flexible during planning Provides opportunity to capture a lot of information

Weaknesses Limited in the information it can capture Does not capture the context of the situation Not flexible during implementation Relies on the truthfulness & memory of respondent

Data Collection: Written Records

Published Statistics Compiled statistics produced and distributed for

public consumption Example: UCR

Nonpublic Agency Records Records kept by agency for processing purposes Not available for public consumption Example: Probation case files

New Data Collected by Agency Staff New information collected as part of the agency

process in order to investigate a research question Example: Use of a new screening tool

Written Records, Continued

Other Related Sources: Content Analysis

Reviewing narratives, usually written, to identify patterns and themes

Example: Newspaper reports of crime over time

Secondary Data Analysis Data are originally collected one set of

researchers and then made available to other researchers for analysis

Example: Arrestee Drug Abuse Monitoring Data

Assessment

Strengths In general, the availability of these data is much

easier than self-report The cost can be significantly less than self-report Conducive to large numbers

Weaknesses Access is sometimes limited especially with regard to

cj information Information is limited by agency priorities Data are rarely flexible and are defined by agency

not the research question Quality of data is sometimes questionable due to

missing and inconsistent reporting of information

Data Collection: Observation

Structured observation=quantitative List of items that an observer will code while

observing behavior Observers use a standard code sheet that

contains items and close-ended responses Items are completed during or immediately

after the observation occurs

Unstructured observation=qualitative General descriptions recorded in a narrative Transcripts of taped descriptions or written

notes used to to identify themes and patterns

Assessment

Strengths Flexible to the needs of the research question Allows for more thorough investigation of certain

situations

Weaknesses Time consuming and expensive Collection of data is potentially impacted by data

collector’s bias Analysis of data can be subjective and open to

bias, especially in the case of unstructured observations

Limited sample size unless extremely well-funded

Multiple Measures

Many studies utilize different types of data to answer research questions For example, using both official and self-report

data to measure variables

Using multiple methods of data collection builds on the strengths of each method individually and minimizes their weaknessesMultiple methods can increase the reliability and validity of the data you collectMultiple methods, however, are often expensive and time-consuming

Deciding Which Method to Use

Decide on your method based on: Research Question: What type of information

does your research question require? Availability/access to the sample: How

available is a sample and what is your access? Size of the sample: How large of a sample do

you need? Time and resources: How much time and

money do you have at your disposal?

Ethical Issues

All research is bounded and defined by professional code of ethicsSocial science research is particularly subject to ethical codes because it almost always includes humans subjectsWhen conducting research, it is necessary to balance the potential benefits from doing the research against the possibility of psychological, emotional, and physical harm

IRBAll human subject research conducted at a University must be reviewed and approved by the Institutional Review BoardThe IRB ensures that federally defined safeguards are applied in all types of research with humans Code of Federal Regulations Title 45, Chapter 46, U.S.

Department of Health & Human Services

Additional rules apply to two populations considered particularly vulnerable: Prisoners Children

IRB Safeguards

Safeguards include: Written consent form must be used to

request participation in the study Written list of benefits and costs of

participation Subject must voluntarily participate Subject must be guaranteed anonymity or

confidentiality Analysis of data in the aggregate Protection from deceit by researchers