Applied Statistics Laboratory
Brain size and autism
Studies have linked brain size in infants and toddlers to a number of future ailments, including autism. One study looked at the brain sizes of 30 autistic boys and 12 non-autistic boys ( the control group), all of whom had undergone an MRI scan as toddlers. The data shown in the following are the whole-brain volumes (in millilitres) from the MRI scans. Investigate whether the mean whole-brain volume in early life is different between autistic and non-autistic boys.
Source: Courchesne, E., et al. (2001), "Unusual brain growth patterns in early life in patients with autistic disorder: an MRI study", Neurology, 57, 245-254
Autistic
1311 1250 1292 1419 1401 1297 1202 1336 1308 1353
1515 1461 1365 1364 1362 1303 1278 1247 1333 1340
1319 1286 1223 1241 1229 1209 1171 1154 1128 1230
Control
1040 1180 1207 1179 1115 1133 1298 1263 1194 1198
1230 1114
Answer all the following questions (See 'Writing Up Your Take-Home Test' in the cover page)
1. Construct the data-frame in EXCEL and import it to "R". For your answer, provide a screen-shot displaying the dataframe in "R".
(Tips: Determine the number of subjects and the number of variables. Include sensible names for the vairables.)
(Instructions for the Screen-shot: Import the data to "R". Display the data frame in "R" by clicking on the "view data set" button. Then, use 'print-screen' (found on your keyboard) to copy the screen with the the data set; control-V to paste it in MS Word; click on the picture, select 'crop' from the 'format' tab and crop the picture; press 'ESC' when finish cropping; resize the picture appropriately.)
2. Construct the appropriate conditional boxplots using "R". Give interpretation of the boxplots.
3. State the aim of the investigation.
4. What is the appropriate statistical procedure for this investigation?
5. Write the null hypothesis in mathematical form; and in plain English.
6. Write the alternative hypothesis in mathematical form; and in plain English.
7. State the model assumption(s) and assess them.
8. Perform the statistical procedure and present (copy and paste) all the results generated by "R". Include all figures, plots and tables, if any.
9. Interpret the p-value.
10. Based on the results of the above statistical procedure, give a conclusion of the study.