6.5.1 - Criminological practical investigation

From the research question to an experiment

A practical needs a question that can be answered by observable data. Here the question is whether context reinstatement and a report-everything instruction increase correct recall compared with a standard open interview after the same neutral film. These are selected cognitive-interview components; the experiment does not test every component of the full technique or professional interviewing competence.

The independent variable is interview procedure: a standard open interview or the cognitive-interview procedure. The dependent variable is the number of distinct correct details recalled, judged against a prepared film key. Record incorrect details and unsupported guesses separately so that gaining more information is not confused with gaining greater accuracy.

A directional hypothesis can predict that the cognitive-interview group will recall more correct details, justified before collection by prior evidence about retrieval cues. The null hypothesis predicts no difference in the distribution of correct-detail scores between procedures. If adequate grounds for direction are absent, use a non-directional prediction and a two-tailed test from the outset.

Use an independent-groups design: each volunteer sees the event once and receives one interview. Randomly allocate recruited people to conditions. This avoids a second recall attempt carrying over information from the first, although individual memory differences may still affect scores. A repeated-measures design reduces participant differences but would require carefully matched events and counterbalancing to address practice, fatigue and event differences. Random allocation is not random sampling of the population.

Recruitment and safeguards before collection

The practical must be ethical in both content and intention: use an ordinary event rather than frightening participants to imitate a crime. A suitable teacher-approved film could show consenting actors arranging books, placing a bag and leaving a room. It should contain no weapons, threat or personally sensitive material. The actors' permission covers filming and the intended classroom use.

Recruit willing adults through an advertisement, or follow the institution's consent and safeguarding arrangements for younger participants. A volunteer sample is feasible, but confidence and interest may differ from the wider population. Participation must not affect grades, friendships or access to teaching. Separate recruitment from any authority who might make refusing uncomfortable. Do not recruit actual victims or ask for experiences of offending for this task.

Explain the harmless content, approximate duration, interview and recording process, data use, confidentiality limits and withdrawal procedure. Participants can stop without giving a reason. Obtain separate recording consent; an anonymous coded written account is an alternative if recording is unnecessary. Store a code-to-identity list separately and securely only while needed for withdrawal, specify a withdrawal deadline before irreversible anonymisation, and delete recordings according to the agreed policy. Debrief participants about the comparison and ordinary memory variation without describing a low score as a personal failing.

Pilot the procedure with approval to check that material, timing and instructions are comprehensible and non-distressing. Stop if unexpected discomfort appears. A debrief is an explanation after a safe procedure, not permission to expose people to distress beforehand.

Standardised tools and data collection

Standardisation lets interview procedure be the planned difference between groups. Prepare a film with a key of unambiguous visible details, the two scripts, consent/debrief forms, a timer, allocation method, coded record sheets and a scoring guide. The guide must accept equivalent descriptions, reject duplicate details and distinguish errors from omissions. For example, if a green bag is placed on a chair, "emerald bag" may be accepted as green; "red bag" is an error, while not mentioning the bag is an omission.

Show the same film with the same screen, seating, volume and viewing duration. One reproducible classroom protocol uses a 60-second film, a five-minute neutral filler task, then a five-minute interview in both conditions. Fix these timings before collection and use the pilot to check feasibility, rather than giving one group extra recall time. Avoid discussion between participants.

In the standard condition, use: "Please describe what you remember happening in the film." In the cognitive condition, use: "Mentally return to the setting and your experience of watching the film. Describe everything you remember, even if a detail seems incomplete or unimportant." Both conditions receive the same instruction to say "I do not know" rather than guess, and the same final neutral prompt: "Is there anything else you remember?" Keep the whole procedure within the agreed interview time and do not add suggestive follow-ups. These are model classroom scripts, not a substitute for professional interview training.