While the numbers certainly do not yet represent a statistically significant random sample (40 and 35 respectively for required students with 3+ sessions), these findings seem to contradict the self-selection bias
that so confounds our attempts to use gross comparisons of students who receive tutoring versus those who don't.
Based on these observations, we concluded that there was no evidence of a self-selection bias
or fear-ofpunishment/embarrassment non-response bias caused by students who chose not to participate in Activity Monitor[TM], or who turned off Activity Monitor[TM] when they were engaged in "inappropriate" behavior.
That is, characteristics that make firms targets of excessive analyst coverage due to analysts' self-selection bias
, arising from investment-banking interests and trading revenues, are not significantly correlated with firms' external financing (investment).
The marginally significant difference on the Rosenberg self-esteem between the experimental and control group also tends to dispel the self-selection bias
Because approximately 31% of the horses in our sample never raced, we correct the regression for self-selection bias
using whether or not the sire ever raced to identify the selection equation.
It's possible that the results reported by Ray and Grimes  contain self-selection bias
as they did not employ any technique to attempt to correct for this.
Another major source of self-selection bias
is from the endogeneity of prenatal care in birthweight production function.
While this approach did not completely overcome the self-selection bias
, the DMV subjects did not have to do anything beyond their planned activities to take part.
Our research also shows that many celebrities exhibit narcissistic behavior prior to becoming famous, which could indicate a self-selection bias
for the entertainment industry by certain personality types," said Young who holds the George Bozanic and Holman G.
Participation was voluntary so a self-selection bias
can't be ruled out, he said.
Equation (1) is then estimated by using OLS, including among the regressors the variable used to adjust for self-selection bias
, LAMBDA, which is obtained from the probit model.
While the methodology included use of data from Medicare claims to adjust for confounding factors, including self-selection bias
, our estimated savings might still have been overstated due to persistent selection effects.