ABSTRACT

Many studies undertaken in the behavioral sciences and related disciplines involve recording the value of a response variable for each subject under more than one condition, on more than one occasion, or both. The subjects may often be arranged in different groups, either those naturally occurring such as gender, or those formed by random allocation, for example, when competing therapies are assessed. Such a design is generally referred to as involving repeated measures. Three examples will help in getting a clearer picture of a repeated measures type of study.

Visual acuity data. This example is one already introduced in Chapter 2, involving response times of subjects using their right and left eyes when light was flashed through lenses of different powers. The data are given in Table 2.3. Here there are two within subject factors, eye and lens strength.

Field dependence and a reverse Stroop task. Subjects selected randomly from a large group of potential subjects identified as having field-independent or field-dependent cognitive style were required to read two types of words (color and form names) under three cue conditions—normal, congruent, and incongruent. The dependent variable was the time in milliseconds taken to read the stimulus words. The data are shown in Table 5.1. Here there are two within subjects factors, type and cue, and one between subjects factor, cognitive style. Field Independence and a Reverse Stroop Task

b1 Form

b2 Color

Subject

c 1 (N)

c 2 (C)

c 3 (I)

c 1 (N)

c 2 (C)

c 3 (I)

a 1 (Field Independent)

1

191

206

219

176

182

196

2

175

183

186

148

156

161

3

166

165

161

138

146

150

4

206

190

212

174

178

184

5

179

187

171

182

185

210

6

183

175

171

182

185

210

7

174

168

187

167

160

178

8

185

186

185

153

159

169

9

182

189

201

173

177

183

10

191

192

208

168

169

187

11

162

163

168

135

141

145

12

162

162

170

142

147

151

a 2 (Field Dependent)

13

277

267

322

205

231

255

14

235

216

271

161

183

187

15

150

150

165

140

140

156

16

400

404

379

214

223

216

17

183

165

187

140

146

163

18

162

215

184

144

156

165

19

163

179

172

170

189

192

20

163

159

159

143

150

148

21

237

233

238

207

225

228

22

205

177

217

205

208

230

23

178

190

211

144

155

177

24

164

186

187

139

151

163

Note. Response variable is time in milliseconds. N, normal; C, congruent; I, incongruent.

Alcohol dependence and salsolinol excretion. Two groups of subjects, one with severe dependence and one with moderate dependence on alcohol, had their salsolinol excretion levels (in millimoles) recorded on four consecutive days (for those readers without the necessary expertise in chemistry, salsolinol is an alkaloid with a structure similar to heroin). Primary interest centers on whether the groups behaved differently over time. The data are given in Table 5.2. Here there is a single within subject factor, time, and one between subjects factor, level of dependence.

Salsolinol Excretion Rates (mmol) for Moderately and Severely Dependent Alcoholic Patients

Day

Subject

1

2

3

4

Group 1 (Moderate Dependence)

1

0.33

0.70

2.33

3.20

2

5.30

0.90

1.80

0.70

3

2.50

2.10

1.12

1.01

4

0.98

0.32

3.91

0.66

5

0.39

0.69

0.73

2.45

6

0.31

6.34

0.63

3.86

Group 2 (Severe Dependence)

1

2

3

4

7

0.64

0.70

1.00

1.40

8

0.73

1.85

3.60

2.60

9

0.70

4.20

7.30

5.40

10

0.40

1.60

1.40

7.10

11

2.50

1.30

0.70

0.70

12

7.80

1.20

2.60

1.80

13

1.90

1.30

4.40

2.80

14

0.50

0.40

1.10

8.10