A study was conducted in 2010 examining the relationship between alcohol and spousal violence using a sample of male parolees (n = 18). One of the first objectives of the study was to assess the extent of alcohol problems in the parolees' lives. To do this, parolees were asked 20 questions relating to alcohol dependence (e.g., "Do friends or family members tell you that you drink too much?" "Have you wanted to stop drinking but couldn't?"). Based on these questions, these investigators constructed an index measured at the interval/ratio level to quantify the extent of drinking problems in each parolee's life. For the sample, the mean number of alcohol problems obtained from this index 7.09 problems with a sample standard deviation of 6.11 problems.
Construct a 95% confidence interval around the estimated mean number of alcohol problems obtained from this sample.
Mean= 7.09 CI= (the sample mean) + & - Z(s.e.).
N= 18 s.e.= s/
S= 6.11 s.e.= 6.11/^(18-1) = 1.481
95%=(7.09)+ 1.96 (1.481)= 9.992
95% =(7.09) - 1.96 (1.481) = 4.187
CI of 95% = 4.187 to 9.992