 What these results show depends partly on the reliability of the measures. One possible source of error is that this study might exaggerate the relationship between life satisfaction and material attainments through the use of a “ladder” scale for life evaluation, ladders being associated with material aspirations. Errors might also arise through salience biases whereby material concerns might be more easily recalled than other important values, such as whether one has succeeded in having children; or through differences in positivity biases across income levels (perhaps wealthier people tend to be more “positive-responding” than poorer individuals). Another question is whether the affect measures adequately track the various dimensions of people’s emotional lives. However, the results are roughly consonant with other research, so they are unlikely to be entirely an artifact of the instruments used in this  study.[23]  A further point of uncertainty is the causal story behind the correlations—whether the correlates, like psychosocial prosperity, cause happiness; whether happiness causes them; whether other factors cause both; or, as is likely, some combination of the three.