Validity & Reliability Of A Study

Validity & Reliability of a Study design A Presentation

VALIDITY AND RELIABILITY IN RESEARCH FINDINGS 

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Validity means that the conclusions are true. Reliability means that someone else using the same method in the same circumstances should be able to obtain the same findings.

Confounding factors

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Unexpected factors beyond your control might have produced the same effect as the intervention you were studying, thereby making it impossible for you to know whether it was your intervention that produced the impact.

Differential subject loss In various groups 

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The type of subjects who drop out of your study or control groups may be related to some of the characteristics you are studying. Selectivity (or bias) In assigning subjects to various groups

Instrumentation Instrument reactivity: the instrument itself has an effect on the subjects and produces a distorted response. Example  In a survey on alcoholism, you ask school children –“Is your father an alcoholic?" 

Unreliability of instruments 

You want to determine the age of children in your study. You ask the mother or any child in the house, "How old is this child"?"

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Your weighing scale is not adjusted to zero level.

Hawthorne effect 

If a group is being observed to determine the effect of an intervention, the observed change may be due to the fact that the group is being studied rather than due to the intervention.

Strategies to deal with threats to validity 

Control

group.

Observing a control group who are not exposed to the risk factor or intervention reduces threats due to history and Hawthorne effects and confounding factors.

Random assignment of subjects 

to the group. This reduces threat to selectivity.

Before & after measurements. 



This allows us to assess whether there has been selectivity as well as differential loss of subjects. If there has been inevitable loss of subjects, it may enable assessment of the dropouts to determine whether they had peculiar characteristics that distinguished them from those who did not drop out.

Unobtrusive methods of data collection 

and allowing adaptation time for subjects to get used to being observed serve to reduce Hawthorne effects.

Careful design and pretesting of instruments 

reduce bias due to Instrumentation.

Knowledge of environment & events 

enables the researcher to be sensitive to external events that could affect validity (i.e., history).