Hypothesis Testing Chapter 6 Steps for Conducting Scientific

Hypothesis Testing Chapter 6

Steps for Conducting Scientific Research Step 1: Formulate a hypothesis Higher temperatures cause people to be more irritable Step 4: Report the results Step 2: Design a study Step 3: Collect & analyze data

Study Design This study will examine the effects of temperature on irritability. Subjects will be randomly assigned to one of three temperature conditions (low [70 o-72 o], moderate [80 o 82 o], or a high [90 o-92 o] temperature room). While in the room an assistant will irritate the subjects. Subjects will then complete an irritation scale.

Hypotheses The Study Hypothesis Ha: The amount of irritation subjects report will be significantly different among the three temperature conditions. The Null Hypothesis Ho: There will be no significant differences in the amount of irritation reported by the subjects among the three temperature conditions.

Sampling from the Population Sample

Operationalize and Measure Variables n Independent Variable: Temperature ¡ 3 Conditions n n Low (70° - 72°) Medium (80° - 82°) High (90° - 92°) Condition #1 Condition #2 Condition #3 Dependent Variable: Irritation ¡ Operationalized as ratings of irritation in response to assistant n Scale included in Appendix of paper

Irritation Scale During the experiment, how much did the assistant make you feel the following: Not at All A Little Bit Moderately Quite a Bit Extremely irritated or annoyed? 1 2 3 4 5 furiously angry? 1 2 3 4 5 mad? 1 2 3 4 5 so angry you felt like hitting the assistant? 1 2 3 4 5

Creating Scale Scores Subject Condition Item 1 Item 2 Item 3 Item 4 Mean Score 1 3 3 4 5 3 3. 75 2 2 2 3 2. 5 3 1 1 2 1. 5 Subject Condition Mean Irritation Score 1 3 3. 75 2 2 2. 5 3 1 1. 5

Describing the Data x=4 s =. 5 3 4 Condition 3 x=3 s =. 5 5 2 n = 15 Condition 2 Condition 1 n = 15 x=2 s =. 5 1 2 3 3 4 n = 15

Hypothesis Testing x=4 s =. 5 x=2 s =. 5 1 n 2 3 3 4 5 What could cause the difference in ratings between condition 1 and condition 3? ¡ Chance n n ¡ ¡ error individual differences not evenly distributed Confounds The independent variable (treatment)

Did the Results Occur by Chance? The treatment effect F-ratio = Between groups variance + Within groups variance Variation due to chance (error). Typically caused by individual differences in participants By controlling within-group variation, scientists can isolate the effects of the independent variable on the dependent variable (between-groups variance).

Inferential Errors True state of affairs Chance is responsible Null hypothesis decision Fail to reject Reject Chance is not responsible Correct “acceptance” Type II error Type I error Correct rejection

Presenting Tabular Results Table 1 Analysis of Variance for Irritation Source df SS MS F p Irritation(I) 1 640 25. 41 . 001 S within group error 36 94 2. 61 __ __

Presenting Graphic Results (F = 5. 0, p <. 05)