Internal Validity

Internal validity refers to the extent to which any effects found within a study can be considered to be due to the manipulations of the identified independent variable(s). Therefore, a study’s internal validity is dependent upon the ability to control for extraneous variables (Shadish, Cook and Campbell, 2001). Table 3.6 outlines the threats to internal validity identified in Phase One, and the actions taken to address these.

Threat to Internal Validity

Description of this threat Action taken to address the threat

Mortality Participant drop out at any point during the study.

Participants were fully briefed about the intervention and associated research study prior to

119 screening process and b) participation in the intervention. Parents were also provided with a full briefing prior to parental consent for both the screening process and students’ participation in the intervention.

Maturation The extent to which any observed changes are due to typical developmental progress during the study time period. These developments may contribute to fluctuation in the dependent variable.

The use of a wait-list comparison group provides an indication of a ‘natural’ rate of maturation, outside of experimental conditions.

History The development of environmental factors over time, which may impact upon the dependent variable. For example; school-based changes between Time 1 and Time 2.

The use of a wait-list comparison group guards against this threat.

Design contamination

The possibility of wait-list comparison participants benefitting from the

intervention through interaction with and access to intervention condition participants. This is a greater threat in the current study due to all participants being from the same cohort and some participants being

The intervention was delivered in a quiet, closed classroom within the learning support department of the school. The control group participants attended typical timetabled lessons during the intervention

120 from the same tutor groups. period, in a separate

part of the school campus. Session leaders were informed of the need to avoid sharing of intervention information with wait- list participants prior to the completion of the intervention phase. Statistical analyses regarding the progress made by wait-list participants during the initial intervention phase will help highlight any positive changes in the wait-list group that may be attributable to this threat.

Fidelity of intervention

The intervention may not be delivered as intended.

An independent observer undertook fidelity checks to ensure that the

intervention was being delivered as intended. See Section 3.16.1.1.5 below.

Selection The extent to which the groups are equivalent at the beginning of the study

Participants were allocated to

intervention or wait-list conditions on the basis of a matched pairs design, in order to

121 optimise comparability of groupings.

Statistical analyses were undertaken to assess the level of homogeneity between groups prior to the intervention stage.

Ambiguity of causal direction

The extent to which the author can be confident that

manipulation of the IV prompts a fluctuation in the DV.

The use a wait-list comparison group increases the extent to which statistical trends may be attributed to intervention participation. Compensatory equalisation of treatment conditions

When members of the wait- list/non-experimental group attempt to compensate for not receiving the intervention.

Wait-list participants were informed that they would receive the same intervention at a later date, in order to guard against compensatory behaviours.

Compensatory rivalry

When the comparison/control group receive compensatory treatment as a result of not receiving the intervention.

Wait-list participants attended typical timetabled sessions during the intervention phase to minimise the possibility of

compensatory activities. Statistical analyses regarding the progress made by wait- list participants during the initial intervention

122 phase will help

highlight any positive changes in the wait-list group that may be attributable to this threat.

Hawthorne effect The participants may be affected by participation rather than intervention effects.

This possible threat is acknowledged. Experimental participation and contact with the session leaders may lead to possible positive outcomes, as opposed to any outcomes being attributable to the contents of the intervention specifically. The participants’ perceptions regarding those mechanisms which may have led to positive outcomes post- intervention was a key topic discussed within the focus groups in Phase Two of the study.

Table 3.6 – A table of those threats to Internal Validity in Phase One of the current study

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3.16.1.1.5 Treatment integrity

Fidelity checks were undertaken on sessions within the intervention phase. These checks were undertaken by Assistant Educational Psychologists (AEPs). Both AEPs were psychology graduates in their mid twenties (one male, one female) and both were employed by the LA EPS at the time of their involvement. Both had accessed the same CBT professional training as the author (section 3.11.1) with one AEP having previous professional experience as a CBT practitioner with the local IAPT project. AEPs used fidelity checklists, provided by the researcher, to subjectively rate the extent to which they felt each of the activities within a session had been completed. Checklists were developed from the intervention session plans and AEPs provided with copies of the contents and aims of each activity with the sessions, to inform their fidelity checks. AEPs were available to provide fidelity checks on five of the seven sessions; checks were not possible for the pre-session and session two, due to AEP workload. Fidelity checklists are included in appendices 33-37.

AEPs were blind to the experimental hypotheses. This action was taken in order to build upon the recommendations made by Green (2013).