2.4 Validity and Reliability
Validity refers to the relevance of the data, whereas reliability refers to the accuracy of the data. If the data are not relevant, why worry about their accuracy? Compared to a larger sample, a small sample has less accurate responses due to random sampling error, but validity errors are more dangerous than inaccuracy (Table 5).
To minimize total error, first make sure the data will be valid, and then use any remaining money to increase the size of your sample.
Table 6. Data-Collection Methods
|Telephone||Fast InexpensiveUnbiasedNonintrusiveRepresentative||Minimal||Preferred for most uses|