Non-response bias is always a concern with survey studies, since owners not responding may differ in some important way from the respondents.
Although the mechanism by which conditioned reinforcers come to guide responding may differ between the BLA and OFC (personal communication, G. Schoenbaum) DA would appear to be important in both structures.
Hence, the ability to respond to radiation may differ in U251MG and U343MG cells.
Although the response rate to the survey was relatively high, the 40% of invited patients who did not respond to the survey may differ systematically to those who did respond, for example, they may be older, or have more advanced disease.
However, patients responding to such advertisements may differ from patients not responding which leads to selection bias and hampers external validity.
Women who responded to this question may differ from non-responders, for instance in motivation to complete the questionnaire, or in literacy.
Yet just as people respond differently to frightening events, the cues that elicit traumatic memories may differ for different people exposed to the same events.
The non-linear model presented here, however, suggests that the nature and strength of density dependence may be non-linear (i.e. differs between high- and low-density regimes) (Table 1) and, because of this, the manner in which the population responds to climate change may differ depending on if the population is at relatively high or relatively low densities.
The study was also in a hypothetical context and behaviour may differ when responding to a real invitation for cancer screening.
The response rate of 65% could have been higher and it is possible that those who chose to respond may have differed from the non-responders in important ways (for example, by being more motivated by a desire to record positive or negative views about the teaching experience).
