Boothwyn, PA 19061 800-784-4221
www.nkhome.com
On Target
www.ontargetshooting.com
Rifle Basix P.O. Box 49064 Charlotte, NC 28277 704-499-3087
www.riflesbasix.com
Shilen Rifles, Inc. P.O. Box 1300 Ennis, TX, 75120 972-875-5318
www.shilen.com
Sightron Inc. 100 Jeffrey Way, Suite A
Youngsville, NC 27596 919-562-3000
www.sightron.com
Tactical Innovations Inc. 345 Sunrise Rd.
Bonners Ferry, ID 83805 208-267-1585
www.tacticalinc.com
Tactical Solutions 2181 Commerce Ave. Boise, ID 83705 866-333-9901
www.tacticalsol.com
Volquartsen Custom P.O. Box 397 Carroll, IA 51401 712-792-4238
www.volquartsen.com
Winchester Ammunition 427 N. Shamrock St. East Alton, IL 62024 618-258-2000
www.winchester.com
Winks/Texasoft P.O. Box 1169
Cedar Hill, TX 75106-1169
www.texasoft.com
Wolf Performance Ammunition P.O. Box 757
Placentia, CA 92871 888-757-9653
Zanders Sporting Goods P.O. Box 166
Baldwin, IL 62217-0166 800-851-4373
www.gznaders.com
Table 1: CCI .17 Mach 2 Rimfire Velocity Data Independent Group Analysis C:\Program Files\TexaSoft\WINKS SDA 6\CCI .17 Mach 2 Rimfire Velocity
Data.SDA
Grouping variable is SUPPRESSOR Analysis variable is VELOCITY
Group Means and Standard Deviations HMR: mean = 2011.173 s.d. = 41.8551 n = 75 NONE: mean = 1993.32 s.d. = 57.095 n = 75
Mean Difference = 17.85333 S.E. Difference = 8.17451 Test for Equality of Variance
This preliminary test determines which version of the t-test to perform. Test equality of variance: F = 1.86 with (74, 74) D.F. p = 0.004 (two-tail)
Note: Since the p-value for equality of variance is low, (less than 0.05) use the Unequal variance t-test results.
Independent Group t-test Hypotheses Ho: There is no difference between means. Ha: The means are different.
Independent Group t-test on VELOCITY
Equal variance: Calculated t= 2.18 with 148 D.F. p = 0.031 (two-tail) Unequal variance: Calculated t= 2.18 with 135.7 D.F. p = 0.031 (two-tail)
(For a one-sided test, you must adjust the p-value according to the direction of your alternative hypothesis.) Confidence Interval
A 95% Confidence Interval about the mean difference is: (1.692 to 34.0147) CI is based on a standard error of 8.1745 and a tabled t-value of 1.977 with 148 d.f.
Effect Size Measures
Cohen's d = 0.359, a medium effect size. (Ref: Rosenthal and Rosnow, 1991) Hedge's g = 0.357 (an adjustment of Cohen's d for sample sizes <10.)
Possible Writeup A preliminary test for equality of variance indicates that the variances of the two groups are significantly different. Therefore a two- sample t-test was performed that does not assume equal variances.
The means of the two groups were significantly different. Using the unequal variances t-test, t(135.7) = 2.18, p = 0.031 Statistics were performed using WINKS SDA Software (Texasoft, Cedar Hill, TX.) Statistical decisions were made at p=0.05 unless otherwise stated.
For these data, the Mean(SD) of VELOCITY for SUPPRESSOR = HMR is 2011.173(41.8551), N= 75, and the Mean(SD) of VELOCITY for SUPPRESSOR = NONE is 1993.32(57.0950), N= 75.
(Results must be interpreted in the context of the practical {i.e. clinical} implications of any observed differences.) Page 168
July — September 2011
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