Campbell and Stanley point out that adherence to experimentation dominated the field of education through the 1920s (Thorndike era) but this gave way to great pessimism and rejection by the late 1930s. However, it ought to be noted that a departure from experimentation to composition writing or essay-writing (Thorndike to Gestalt Psychology) happened most frequently by individuals already adept at the experimental tradition.
Therefore we have to know about the past so that we avert total rejection of any method, and instead take a serious look at the effectiveness and applicability of current and past methods without making false assumptions.
Multiple experimentations are much more typical of science compared to a once and for all definitive experiment! Experiments really need replication and cross-validation at different times and conditions before the results can be theoretically interpreted with confidence.
An interesting point made is that experiments that produce conflicting theories contrary to each other likely will not have clear-cut results that actually both researchers have observed something legitimate which reflects the truth.
Adopting experimentation in education shouldn’t imply advocating a situation incompatible with traditional wisdom, rather experimentation may be seen as a process of refining this knowledge. Therefore such regions, cumulative science, and wisdom, must not be conflicting forces.
Why inner validity issues
Internal validity creates the conclusions of a causal relationship credible and trustworthy.
The Way to assess whether your study has internal validity
There are three essential conditions for internal validity. All three conditions must happen to establish causality between an independent factor A (your therapy factor) and a dependent variable B (your answer variable).
Your treatment and response variables change together.
Your treatment precedes changes in your response variables No perplexing or extraneous factors can describe the results of your research. From the research example above, only two out of those 3 conditions are met.
Brewed java and memory functionality improved together. Drinking coffee happened before the memory test. The time of day of the sessions is an extraneous factor that can evenly explain the results of the analysis.
Because you assigned participants to groups depending on the schedule, the groups have been distinct at the start of the study. Any gaps in-memory performance might be due to a difference in the good time of day. Therefore, you cannot state for certain whether the time of day or drinking a cup of coffee enhanced memory performance.
That means your study has low internal validity, and you can’t deduce a causal relationship between drinking coffee and memory performance.
The trade-off between external and internal validity
External validity is the degree to which you can research the findings of a study to other steps, settings, or groups. In other words, can you apply the findings of your study to a wider context?
There’s an inherent trade-off between external and internal validity; the more you control extraneous factors in your research, the less you can generalize your findings into a broader context.
Research example In your study of java and memory and the external validity is contingent on the selection of the memory test, the participant inclusion criteria, and the laboratory setting.
Threats to internal validity are important to recognize and offset in a study design for a strong study.
Research example (single-group): A research team wants to research whether having indoor plants on office desks boosts the growth of IT employees from a business. The researchers give every one of the participating IT workers a plant to set by their background for the month-long study. All participants complete a timed productivity task before (pre-test) and after the analysis (post-test).
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